x86/efi: Implement a __efi_call_virt macro

For i386, all the EFI system runtime services functions return efi_status_t
except efi_reset_system_system. Therefore, not all functions can be covered
by the same macro in case the macro needs to do more than calling the function
(i.e., return a value). The purpose of the __efi_call_virt macro is to be used
when no return value is expected.

For x86_64, this macro would not be needed as all the runtime services return
u64. However, the same code is used for both x86_64 and i386. Thus, the macro
__efi_call_virt is also defined to not break compilation.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Borislav Petkov <bp@suse.de>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>