spi: bcm2835: Restore native CS probing when pinctrl-bcm2835 is absent

spi: bcm2835: Restore native CS probing when pinctrl-bcm2835 is absent

The lookup table forces the use of the "pinctrl-bcm2835" GPIO chip
provider and essentially assumes that there is going to be such a
provider, and if not, we will fail to set-up the SPI device.

While this is true on Raspberry Pi based systems (2835/36/37, 2711,
2712), this is not true on 7712/77122 Broadcom STB systems which use the
SPI driver, but not the GPIO driver.

There used to be an early check:

       chip = gpiochip_find("pinctrl-bcm2835", chip_match_name);
       if (!chip)
               return 0;

which would accomplish that nicely, bring something similar back by
checking for the compatible strings matched by the pinctrl-bcm2835.c
driver, if there is no Device Tree node matching those compatible
strings, then we won't find any GPIO provider registered by the
"pinctrl-bcm2835" driver.

Fixes: 21f252cd29f0 ("spi: bcm2835: reduce the abuse of the GPIO API")
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20250401233603.2938955-1-florian.fainelli@broadcom.com
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>