USB: xhci: correctly enable interrupts

xhci has its own interrupt enabling routine, which will try to
use
MSI-X/MSI if present. So the usb core shouldn't try to enable
legacy
interrupts; on some machines the xhci legacy IRQ setting
is
invalid.

v3: Be careful to not break XHCI_BROKEN_MSI workaround (by
trenn)

Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Oliver Neukum
<oneukum@suse.de>
Cc: Thomas Renninger <trenn@suse.de>
Cc: Yinghai Lu
<yinghai@kernel.org>
Cc: Frederik Himpe <fhimpe@vub.ac.be>
Cc: David
Haerdeman <david@hardeman.nu>
Cc: Alan Stern
<stern@rowland.harvard.edu>
Acked-by: Sarah Sharp
<sarah.a.sharp@linux.intel.com>
Reviewed-by: Thomas Renninger
<trenn@suse.de>
Signed-off-by: Hannes Reinecke
<hare@suse.de>
Signed-off-by: Greg Kroah-Hartman
<gregkh@linuxfoundation.org>

idea is taken here -
https://github.com/varunchitre15/thunderzap_xl/commit/dc8e48e161b612ffc7e0b912ace0997102942b1f