usb: xhci-plat: Remove usage of PM suspend/resume

Commit 57d04eb1 ("usb: xhci: add the suspend/resume functionality")
added PM suspend/resume functionality with xHCI platform driver and not
handling case when xHCI platform driver is using PM runtime suspend/resume
functionality. MSM related host mode functionality is having PM runtime
suspend/resume supported which uses same xhci_suspend() and xhci_resume()
API used with xhci_pm_suspend() and xhci_pm_resume() functionality. Fix
unclock access when system suspend context xhci_pm_suspend() is calling
xhci_suspend() as XHCI is already runtime suspended.

Change-Id: Iafbd5ef4d67dfc2cf89213e8f296f6d9ade8feab
Signed-off-by: Mayank Rana <mrana@codeaurora.org>