msm: Kconfig: Enable RPM stats flag

Enable RPM stats flag, which provides statistical information
of low power mode that RPM enters. The stats will be available
via debufs entry.

Change-Id: If3a6a7be010f60f5f64169d961c715e515d1bf8a
Signed-off-by: Girish S Ghongdemath <girishsg@codeaurora.org>