MIPS: OCTEON: octeon-usb: use common gpio_bit definition

cvmx_gpio_bit_cfgx bitfields are indentical on cn70xx and cn73xx,
and also match the default definition. So use that instead.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org