Mailbox functions and interrupts are only for Navi12 VF.

Register functions and irqs during initialization.
Reviewed-by: NEmily Deng <Emily.Deng@amd.com>
Signed-off-by: NJiange Zhao <Jiange.Zhao@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>