Driver uses GPIO functions but doesn't include the header explcitly. Add
that to fix build errors when GPIOLIB is disabled.

drivers/phy/allwinner/phy-sun4i-usb.c:367:11: error: implicit
declaration of function ‘gpiod_get_value_cansleep’; did you mean
‘gpio_get_value_cansleep’? [-Werror=implicit-function-declaration]
drivers/phy/allwinner/phy-sun4i-usb.c:707:22: error: implicit
declaration of function ‘devm_gpiod_get_optional’; did you mean
‘devm_clk_get_optional’? [-Werror=implicit-function-declaration]
drivers/phy/allwinner/phy-sun4i-usb.c:708:11: error: ‘GPIOD_IN’
undeclared (first use in this function); did you mean ‘GPIOF_IN’?
drivers/phy/allwinner/phy-sun4i-usb.c:815:21: error: implicit
declaration of function ‘gpiod_to_irq’; did you mean ‘gpio_to_irq’?
[-Werror=implicit-function-declaration]
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Link: https://lore.kernel.org/r/20200716062427.71763-1-vkoul@kernel.org