drm/i915/dmabuf: fix broken build

wbinvd_on_all_cpus() is only defined on x86 it seems, plus we need to
include asm/smp.h here.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211021125332.2455288-1-matthew.auld@intel.com