msm_serial_hs: Support out of band sleep feature

During clock off operation flow control lines and wakeup
interrupt should be disabled for out of band sleep
mechanism.

Change-Id: I1c6d917ccf3aadef7d7756e47e674e963e5b2c72
Signed-off-by: Dilip Kota <c_dkota@codeaurora.org>