dwc3-msm: Add support to disable device mode PM runtime

High speed phy suspend is not supported on emulation target.
Hence add support to keep PM runtime disabled which prevents
phy to enter low power mode.

Change-Id: Iaa21ece3a58d4da6b03699bd068d01f2fba85343
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>