power domain: MediaTek: add power domain driver for MT7629 SoC

power domain: MediaTek: add power domain driver for MT7629 SoC

This adds a power domain driver for the Mediatek SCPSYS unit.

The System Control Processor System (SCPSYS) has several power
management related tasks in the system. The tasks include thermal
measurement, dynamic voltage frequency scaling (DVFS), interrupt
filter and lowlevel sleep control. The System Power Manager (SPM)
inside the SCPSYS is for the MTCMOS power domain control.

For now this driver only adds power domain support.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Reviewed-by: Simon Glass <sjg@chromium.org>