ARM: msm: dts: Add flag to not switch PLLs during retention for MSM8992

On 8992, there is no need to switch to the global pll when the
cpu is in retention. The cpus are capable of going in and out of
retention while still on the HFPLL. Add a flag to indicate to the
driver that the cpu clock need not be ramped down and switched to
global pll when going into retention.

Change-Id: I480b3c1dce09e8a3f5f241fca16f617083bd5827
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>