regulator: qcom_spmi: Add support for SAW

Add support for SAW controlled regulators.
The regulators defined as SAW controlled in the device tree
will be controlled through special CPU registers instead of direct
SPMI accesses.
This is required especially for CPU supply regulators to synchronize
with clock scaling and for Automatic Voltage Switching.

Signed-off-by: Ilia Lin <ilialin@codeaurora.org>