usb: common: Patch simplify usb_decode_set_clear_feature function.

Patch adds usb_decode_test_mode and usb_decode_device_feature functions,
which allow to make more readable and simplify the
usb_decode_set_clear_feature function.

Signed-off-by: Pawel Laszczak <pawell@cadence.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>