drivers: soc: qcom: system_stats: Support for System stats

RPM stats and RPM master stats provide the similar information via
different interfaces. Combine them into a single driver to provide a
unified information.

Change-Id: If5a5ef6e080ab6d75139472c5204eb6d5e9c6614
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>