soc: qcom: rpm_stats: Add support to display multiple records

RPM stats drivers currently displays 2 records. Add support
to display multiple records using sysfs.

Also remove unused code and add remove method for proper cleanup
during driver unbind.

Change-Id: I251fcdd3434de2125f72acd2202e7152f7937f65
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>