soc: mediatek: mtk-svs: Enable the IRQ later

soc: mediatek: mtk-svs: Enable the IRQ later

If the system does not come from reset (like when is booted via
kexec()), the peripheral might triger an IRQ before the data structures
are initialised.

Fixes:

[    0.227710] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000f08
[    0.227913] Call trace:
[    0.227918]  svs_isr+0x8c/0x538

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Link: https://lore.kernel.org/r/20221127-mtk-svs-v2-0-145b07663ea8@chromium.org
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>