ipq40xx: chromium: Support Chromium "crossystem" GPIO tooling

ChromiumOS's vboot_reference tooling [1] provides convenient access to
various firmware and hardware details via its `crossystem` tool.
crossystem currently:
(1) relies on the v1 GPIO cdev API to read GPIOs; and
(2) expects gpio-line-names properties.

Enable the kernel config, and document a few pins for Google WiFi
devices.

I only go so far as to pull two relevant names out of the vendor device
tree. Others could perhaps be backfilled if the info is available and
useful.

[1] https://chromium.googlesource.com/chromiumos/platform/vboot_reference/+/HEAD/README

Signed-off-by: Brian Norris <[email protected]>
Link: openwrt/openwrt#16014
Signed-off-by: Robert Marko <[email protected]>

target/linux/ipq40xx/chromium/config-default

@@ -1,4 +1,5 @@
 CONFIG_BLK_DEV_SD=y
+CONFIG_GPIO_CDEV_V1=y
 CONFIG_SCSI=y
 CONFIG_SCSI_COMMON=y
 CONFIG_SG_POOL=y

target/linux/ipq40xx/files-6.6/arch/arm/boot/dts/qcom/qcom-ipq4019-wifi.dts

@@ -74,6 +74,67 @@
 };
 
 &tlmm {
+	gpio-line-names = "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  "",
+			  /* AP_FLASH_WP_L is crossystem ABI. */
+			  "AP_FLASH_WP_L" /* 53 */,
+			  "",
+			  "",
+			  "",
+			  /* RECOVERY_SW_L is crossystem ABI. */
+			  "RECOVERY_SW_L" /* 57 */;
+
 	fw_pinmux: fw_pinmux {
 		wp {
 			pins = "gpio53";