drivers: qcom: subsystem_sleep_stats: Reuse apss stats if available

rpmh_master_stats driver maintained apss master stats. If it does
apss_master_stats.version_id get updated to non-zero value.

This change adds support to reuse already calculated data. Also
while doing this converts duration(ticks) to msec.

Change-Id: I5a1db5cc9543deba68e3c047223f6e93c635b733
Signed-off-by: Tushar Nimkar <tnimkar@codeaurora.org>