msm: idle: Use ARM suspend/resume APIs to restore during warmboot

ARM generic cpu_suspend/resume APIs restore the necessary CP15 registers
to a known state when resuming from a reset state. Use of generic
suspend/resume APIs allows the msm warmboot code to not care about
restoring core registers used by ARM kernel. Also, the PM subsystem no
longer needs to allocate page table or uncached memory to save CPU
registers.

While at it convert most of the assembler code into respective C
function except for warmboot code that executes with MMU turned off.
Also, the idle subsystem no longer needs to manage a  page table or
uncached memory to save CPU registers.

Change-Id: I78a75d0a3c703390eec476199c7ca2786360e12a
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>