scsi: ufs: Add runtime PM support for UFS host controller driver

Add runtime PM helpers to suspend/resume UFS controller at runtime.
Enable runtime PM by default for pci and platform drivers as the
initialized hardware can suspend if it is not used after bootup.

Change-Id: I70b8f7ab9c5a806234701a5eb7735910ee6d052e
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>