UefiCpuPkg: Add RISCV_EFI_BOOT_PROTOCOL related definitions

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4076



RISC-V UEFI based platforms need to support RISCV_EFI_BOOT_PROTOCOL.
Add this protocol GUID definition and the header file required.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Daniel Schaefer <git@danielschaefer.me>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Acked-by: Abner Chang <abner.chang@amd.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Andrei Warkentin <andrei.warkentin@intel.com>
Acked-by: Ray Ni <ray.ni@intel.com>