lib: sbi: Extend sbi_system_reset() for domains

The sbi_system_reset() should issue platform system reset only if
domain of current HART is allowed to do system reset.

This patch extends sbi_system_reset() as-per above.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>