soc: amlogic: Add support for Secure power domains controller

Add support for the Amlogic Secure Power controller. In A1/C1 series, power
control registers are in secure domain, and should be accessed by smc.

Signed-off-by: Jianxin Pan <jianxin.pan@amlogic.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/1579087831-94965-4-git-send-email-jianxin.pan@amlogic.com