[target/msm8660_surf]: Add keypad driver support.

Add code to interface with PMIC SSBI arbiter registers to scan keypad for
msm8660 target. Add two additional functions to read, write and configure
the PMIC gpios used for keypad. Add code to use different read/write functions
for PMIC SSBI2 interface for msm7630 and PMIC arbiter wrapper interface for
msm8660 target.

Change-Id: Idde16232785dfc06728dea29c05b99251e45ba9f
7 files changed