lib: sbi: system reset with invalid parameters

The SBI specification requires that sbi_system_reset() returns
SBI_ERR_INVALID_PARAM if reset_type or reset_reason are not valid.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Xiang W <wxjstz@126.com>