spi: bcm2835: Add GPIOLIB dependency

Fix:

drivers/spi/spi-bcm2835.c: In function 'chip_match_name':
drivers/spi/spi-bcm2835.c:356:21: error:
			dereferencing pointer to incomplete type
drivers/spi/spi-bcm2835.c: In function 'bcm2835_spi_setup':
drivers/spi/spi-bcm2835.c:382:2: error:
	`		implicit declaration of function 'gpiochip_find'
drivers/spi/spi-bcm2835.c:387:21: error:
			dereferencing pointer to incomplete type

by adding the now mandatory GPIOLIB dependency.

Fixes: a30a555d ("spi: bcm2835: transform native-cs to gpio-cs
	on first spi_setup")
Cc: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Mark Brown <broonie@kernel.org>