spi: pxa2xx: Convert to GPIO descriptor API where possible

We still need to request/free GPIOs passed via the legacy path of
pxa2xx_spi_chip::gpio_cs, but we can use the gpiod API otherwise.

Consistently use the descriptor API instead of the legacy one.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>