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: 21f252c ("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>

drivers/spi/spi-bcm2835.c

@@ -1226,7 +1226,12 @@ static int bcm2835_spi_setup(struct spi_device *spi)
 	struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr);
 	struct bcm2835_spidev *target = spi_get_ctldata(spi);
 	struct gpiod_lookup_table *lookup __free(kfree) = NULL;
-	int ret;
+	const char *pinctrl_compats[] = {
+		"brcm,bcm2835-gpio",
+		"brcm,bcm2711-gpio",
+		"brcm,bcm7211-gpio",
+	};
+	int ret, i;
 	u32 cs;
 
 	if (!target) {
@@ -1291,6 +1296,14 @@ static int bcm2835_spi_setup(struct spi_device *spi)
 		goto err_cleanup;
 	}
 
+	for (i = 0; i < ARRAY_SIZE(pinctrl_compats); i++) {
+		if (of_find_compatible_node(NULL, NULL, pinctrl_compats[i]))
+			break;
+	}
+
+	if (i == ARRAY_SIZE(pinctrl_compats))
+		return 0;
+
 	/*
 	 * TODO: The code below is a slightly better alternative to the utter
 	 * abuse of the GPIO API that I found here before. It creates a