RISC-V: KVM: Rename the SBI_STA_SHMEM_DISABLE to a generic name

RISC-V: KVM: Rename the SBI_STA_SHMEM_DISABLE to a generic name

SBI_STA_SHMEM_DISABLE is a macro to invoke disable shared memory
commands. As this can be invoked from other SBI extension context
as well, rename it to more generic name as SBI_SHMEM_DISABLE.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240420151741.962500-7-atishp@rivosinc.com
Signed-off-by: Anup Patel <anup@brainfault.org>