mailbox: add control_by_sw for mt8195

To make sure the GCE request signal to SPM is not trigger by
other HW modules and cause suspend premature wake.

Set 0x7 (the bit 0~2 as 1) to GCE_GCTL_VALUE, to configure the
request signal control by SW and release the request to SPM.

Signed-off-by: jason-jh.lin <jason-jh.lin@mediatek.com>
Reviewed-by: Tzung-Bi Shih <tzungbi@google.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>