virtchnl: Add missing explicit padding to structures

On e.g. m68k, the alignment of 32-bit values is only 2 bytes, leading
to the following:

    ./include/linux/avf/virtchnl.h:147:36: warning: division by zero [-Wdiv-by-zero]
      { virtchnl_static_assert_##X = (n)/((sizeof(struct X) == (n)) ? 1 : 0) }
					^
    ./include/linux/avf/virtchnl.h:577:1: note: in expansion of macro ‘VIRTCHNL_CHECK_STRUCT_LEN’
     VIRTCHNL_CHECK_STRUCT_LEN(272, virtchnl_filter);
     ^~~~~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/avf/virtchnl.h:577:32: error: enumerator value for ‘virtchnl_static_assert_virtchnl_filter’ is not an integer constant
     VIRTCHNL_CHECK_STRUCT_LEN(272, virtchnl_filter);
				    ^~~~~~~~~~~~~~~
    ./include/linux/avf/virtchnl.h:147:53: note: in definition of macro ‘VIRTCHNL_CHECK_STRUCT_LEN’
      { virtchnl_static_assert_##X = (n)/((sizeof(struct X) == (n)) ? 1 : 0) }
							 ^
    ./include/linux/avf/virtchnl.h:147:36: warning: division by zero [-Wdiv-by-zero]
      { virtchnl_static_assert_##X = (n)/((sizeof(struct X) == (n)) ? 1 : 0) }
					^
    ./include/linux/avf/virtchnl.h:619:1: note: in expansion of macro ‘VIRTCHNL_CHECK_STRUCT_LEN’
     VIRTCHNL_CHECK_STRUCT_LEN(16, virtchnl_pf_event);
     ^~~~~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/avf/virtchnl.h:619:31: error: enumerator value for ‘virtchnl_static_assert_virtchnl_pf_event’ is not an integer constant
     VIRTCHNL_CHECK_STRUCT_LEN(16, virtchnl_pf_event);
				   ^~~~~~~~~~~~~~~~~
    ./include/linux/avf/virtchnl.h:147:53: note: in definition of macro ‘VIRTCHNL_CHECK_STRUCT_LEN’
      { virtchnl_static_assert_##X = (n)/((sizeof(struct X) == (n)) ? 1 : 0) }
							 ^
    ./include/linux/avf/virtchnl.h:147:36: warning: division by zero [-Wdiv-by-zero]
      { virtchnl_static_assert_##X = (n)/((sizeof(struct X) == (n)) ? 1 : 0) }
					^
    ./include/linux/avf/virtchnl.h:640:1: note: in expansion of macro ‘VIRTCHNL_CHECK_STRUCT_LEN’
     VIRTCHNL_CHECK_STRUCT_LEN(12, virtchnl_iwarp_qv_info);
     ^~~~~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/avf/virtchnl.h:640:31: error: enumerator value for ‘virtchnl_static_assert_virtchnl_iwarp_qv_info’ is not an integer constant
     VIRTCHNL_CHECK_STRUCT_LEN(12, virtchnl_iwarp_qv_info);
				   ^~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/avf/virtchnl.h:147:53: note: in definition of macro ‘VIRTCHNL_CHECK_STRUCT_LEN’
      { virtchnl_static_assert_##X = (n)/((sizeof(struct X) == (n)) ? 1 : 0) }
							 ^
    ./include/linux/avf/virtchnl.h:147:36: warning: division by zero [-Wdiv-by-zero]
      { virtchnl_static_assert_##X = (n)/((sizeof(struct X) == (n)) ? 1 : 0) }
					^
    ./include/linux/avf/virtchnl.h:647:1: note: in expansion of macro ‘VIRTCHNL_CHECK_STRUCT_LEN’
     VIRTCHNL_CHECK_STRUCT_LEN(16, virtchnl_iwarp_qvlist_info);
     ^~~~~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/avf/virtchnl.h:647:31: error: enumerator value for ‘virtchnl_static_assert_virtchnl_iwarp_qvlist_info’ is not an integer constant
     VIRTCHNL_CHECK_STRUCT_LEN(16, virtchnl_iwarp_qvlist_info);
				   ^~~~~~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/avf/virtchnl.h:147:53: note: in definition of macro ‘VIRTCHNL_CHECK_STRUCT_LEN’
      { virtchnl_static_assert_##X = (n)/((sizeof(struct X) == (n)) ? 1 : 0) }
							 ^

Fix this by adding explicit padding to structures with holes.

Reported-by:  <noreply@ellerman.id.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>