spi: pic32: Convert to use GPIO descriptors

The driver already relies on the core looking up GPIO lines
from the core, so this is trivial to switch over to using
GPIO descriptors.

Cc: Purna Chandra Mandal <purna.mandal@microchip.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220122004846.374930-1-linus.walleij@linaro.org


Signed-off-by: Mark Brown <broonie@kernel.org>