net: smc91x: Fix build without gpiolib

If GPIOLIB=n the following build errors occur:

drivers/net/ethernet/smsc/smc91x.c: In function 'try_toggle_control_gpio':
drivers/net/ethernet/smsc/smc91x.c:2204:2: error: implicit declaration of function 'devm_gpiod_get_index' [-Werror=implicit-function-declaration]
drivers/net/ethernet/smsc/smc91x.c:2204:7: warning: assignment makes pointer from integer without a cast [enabled by default]
drivers/net/ethernet/smsc/smc91x.c:2213:2: error: implicit declaration of function 'gpiod_direction_output' [-Werror=implicit-function-declaration]
drivers/net/ethernet/smsc/smc91x.c:2216:3: error: implicit declaration of function 'devm_gpiod_put' [-Werror=implicit-function-declaration]
drivers/net/ethernet/smsc/smc91x.c:2222:2: error: implicit declaration of function 'gpiod_set_value_cansleep' [-Werror=implicit-function-declaration]

Fix this by letting the driver depend on GPIOLIB if OF is selected.

Fixes: 7d2911c4 ("net: smc91x: Fix gpios for device tree based booting")
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>