usb: XHCI: Do not allow enabling MSI from XHCI

As part of Host controller initialization XHCI tries to
enable MSI if CONFIG_PCI is defined. This is causing host
controller driver initialization failure. As MSM has PCI-e
core independent of XHCI core hence disallow XHCI to enable
MSI.

Change-Id: Ie934bc642f12aade269283ff62baf00bc26d0282
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>