ASoC: pxa: add GPIOLIB_LEGACY dependency

ASoC: pxa: add GPIOLIB_LEGACY dependency

The pxa27x platform uses the legacy gpiolib interfaces, including
in its sound drivers:

sound/arm/pxa2xx-ac97-lib.c: In function 'pxa2xx_ac97_hw_probe':
sound/arm/pxa2xx-ac97-lib.c:374:23: error: implicit declaration of function 'gpio_request_one' [-Wimplicit-function-declaration]
  374 |                 ret = gpio_request_one(reset_gpio, GPIOF_OUT_INIT_HIGH,

Make sure we don't select those drivers for compile-testing unless
we are building for a pxa27x system, or CONFIG_GPIOLIB_LEGACY is
already enabled.

The SND_PXA_SOC_SSP driver accidentally used a dependency on PLAT_PXA,
which includes both ARCH_PXA and ARCH_MMP, but it is only used on
the former.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20250808151822.536879-21-arnd@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>