USB: xhci: Avoid global namespace pollution.

Make all globally visible functions start with xhci_ and mark functions as
static if they're only called within the same C file.  Fix some long lines
while we're at it.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>