ARM: dts: msm: Enable RPM PC when mutiple cores are online

Add DTS flag to enable RPM PC when multiple cores are online. This
ensures that the system low power modes are synchornized when cores are
entering/exiting idle PC.

Change-Id: I66b94c74ba2ec5e8dd9926abc22f8aba153cb694
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>