arm: mach-msm: remove ARCH-specific dependency from USB

ARCH-specific dependencies should not belong in the USB Kconfig
file.  Rather, it should be the other way around: the ARCH's
Kconfig should select USB_ARCH_HAS_XHCI.

Also add support for XHCI to ARCH_APQ8084.

Change-Id: I9ad1dab169a985ebf732b9b224613e44e5ec9d17
Signed-off-by: Jack Pham <jackp@codeaurora.org>