usb: phy: phy-generic: No need to call gpiod_direction_output() twice

Commit 9eb07977 ("usb: phy: generic: fix the gpios to be optional")
calls gpiod_direction_output() in the probe function, so there is no need to
call it again, as we can simply call gpiod_set_value() directly.

Also, in usb_gen_phy_shutdown() we can simply put the GPIO directly in its
active level state and this allows us to simplify the nop_reset function to
treat only the reset case.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>