question about RISCV EFI stub support

[Kefeng Wang]

Hi Atish and Ard,

The commit "cb7d2dd5612a RISC-V: Add PE/COFF header for EFI stub" use 
c.li to

add Magic "MZ" signature for PE/COFF header, which select RISCV_ISA_C, 
but "C"

to the ISA is optional,  and if "C" is not support ,  EFI boot is not 
supported.

Could we use ".word MZ_MAGIC" like x86 code or some other way to support 
"MZ" signature?

Thanks,

Kefeng