KVM: riscv: selftests: Move sbi definitions to its own header file

KVM: riscv: selftests: Move sbi definitions to its own header file

The SBI definitions will continue to grow. Move the sbi related
definitions to its own header file from processor.h

Suggested-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20240420151741.962500-18-atishp@rivosinc.com
Signed-off-by: Anup Patel <anup@brainfault.org>