msm: pm: warmboot entry/exit counters on IMEM

Add warmboot entry/exit counters for each core on a non-cacheable always
on IMEM memory. This is a useful feature during debug to understand if
the system has correctly warmbooted after a power collapse. The debug
counters start at a memory offset of 0x664 on the IMEM. Each core
reserves 4 words for events, of which 3 are being used to monitor the
following events,
1) power collapse entry
2) warmboot exit
3) failed power collapse when wfi returns with a pending interrupt.

Change-Id: I45aac8e4a4d3421d586790b3b66fd71a8d88ea9d
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>