usb: xhci-msm-hsic: Define XHCI_PLAT quirk

This patch adds the XHCI_PLAT quirk to xhci-msm-hsic to denote that
it is a platform_driver and simultaneously reverts commit 1885eed5
"usb: XHCI: Do not allow enabling MSI from XHCI" since PCI interrupts
are now only enabled when the XHCI_PLAT quirk is disabled.

Change-Id: Ia2a1aadd3f574b89da6e0715e3e4afbf162e8b19
Signed-off-by: Jack Pham <jackp@codeaurora.org>