net: ti: cpsw: include gpio/consumer.h

On platforms that don't always enable CONFIG_GPIOLIB, we run into
a build failure:

drivers/net/ethernet/ti/cpsw.c: In function 'cpsw_probe':
drivers/net/ethernet/ti/cpsw.c:3006:9: error: implicit declaration of function 'devm_gpiod_get_array_optional' [-Werror=implicit-function-declaration]
  mode = devm_gpiod_get_array_optional(&pdev->dev, "mode", GPIOD_OUT_LOW);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/ti/cpsw.c:3006:59: error: 'GPIOD_OUT_LOW' undeclared (first use in this function); did you mean 'GPIOF_INIT_LOW'?
  mode = devm_gpiod_get_array_optional(&pdev->dev, "mode", GPIOD_OUT_LOW);

Since we cannot rely on this to be visible from gpio.h, we have to include
gpio/consumer.h directly.

Fixes: 2652113f ("net: ethernet: ti: Allow most drivers with COMPILE_TEST")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>