msm: pm-8x60: save and restore CP15 registers

To prevent the Krait core configuration from being indvertently changed
when doing L2 power collapse, save a few CP15 registers and restore them
back after coming out of power collapse. This needs to be done after
switching the Krait from active freq to QSB clock source.

Before doing power collapse, the core0 clock switches over to QSB. However,
QSB can run at any frequency and the voltage required for that
frequency, needs to be ensured when coming out power collapse. If the
QSB clock at resume, is a higher frequency at than the QSB clock was at
collapse, then we may run the risk of running at higher clock with a
lower voltage.

Hence, switch to 1.0 V (safe vdd) when going into PC (after switching to
QSB clock source) and the SPM would resume at 1.0V. After the core
starts running, restore the CP15 registers and switch to the previously
saved active voltage, before switching clocks to the active frequency.

This is applicable only for APQ8064.

Change-Id: I75a70f5e07bd581fc8028bed79de7ee796f4c411
Signed-off-by: Praveen Chidambaram <pchidamb@codeaurora.org>