xHCI: test and clear RWC bit

Introduce xhci_test_and_clear_bit() to clear RWC bit in PORTSC register.

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