efi_loader: struct efi_configuration_table

Commit 393fccdf6c73 ("efi_loader: efi_guid_t must be 64-bit aligned")
has changed the alignment of efi_guid_t. This changed the size of
struct efi_configuration_table on 32-bit systems form 20 to 24 bytes. As
an array of this type is pointed to by the system table this breaks
compatibility with existing versions of GRUB and Linux. Let's get back the
original size by using the attribute __packed.

Fixes: 393fccdf6c73 ("efi_loader: efi_guid_t must be 64-bit aligned")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>