ARM: dts: msm: add proxy voter for QRD SDM660

pm660_ldo10 supplies power for multiple consumers including UFS.
The load from UFS is invisible for the regulator before the driver
voted it. Any other light load consumers would vote its load and
force the regulator entering into LPM mode which cause OCP triggered.
Add proxy voter for pm660_ldo10 to track this existing UFS load.

Change-Id: I32759025e0349858eaafb6a3b062a6c64314ccfe
Signed-off-by: Yingwei Zhao <cyizhao@codeaurora.org>