drivers: qcom: add system PM violators debug driver

Add driver to read MSGRAM and list the DRVs preventing system low power
modes.

sys_pm_violators stats can enabled by writing the mode (cxpc, aoss or
ddr) and periodicity of stats and triggering the AOP to record the stats
by writing to the 'aop_send_message' node.

Example:
echo "{class: lpm_mon, type: cxpc, dur: 1000, flush: 15, ts_adj: 1}" >
	/sys/kernel/debug/aop_send_message

The stats can be read out after the time period by reading the 'stats'
node.

cat /sys/kernel/debug/sys_pm_violators

Change-Id: I9d2501aa19108f015c7381104b2484a0d487cb3f
Signed-off-by: Lina Iyer <ilina@codeaurora.org>