include: pe.h: Add RISC-V related PE definition

Define RISC-V related machine types.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Link: https://lore.kernel.org/r/20200415195422.19866-3-atish.patra@wdc.com


Signed-off-by: Ard Biesheuvel <ardb@kernel.org>