tcl/interface: Find proper alias for RP1 on Raspberry Pi 5

Previously, Linux assigned gpiochip numbers sequentially depending on
when the chip driver was probed. As RP1 is on the end of a PCIe link, it
is probed later than the on-board chips (including expanders connected
over SPI/I2C). This meant that RP1's gpiochip assignment was at an
offset that could potentially change.

A downstream kernel patch now assigns fixed offsets for RP1 and the
onboard gpiochips. Query the device tree to get proper GPIO_CHIP index.

Change-Id: I759978d4b3021c815a7d9febb41961cd1d3d185c
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/8650
Reviewed-by: Jonathan Bell <jonathan@raspberrypi.com>
Tested-by: jenkins

tcl/interface/raspberrypi5-gpiod.cfg

@@ -18,11 +18,19 @@ proc read_file { name } {
 	return $result
 }
 
+proc find_rp1_alias {} {
+	foreach f [glob -directory "/proc/device-tree/aliases" "gpio\[0-9\]"] {
+		if {[string match "*/rp1/*" [read_file $f]]} {
+			return $f
+		}
+	}
+}
+
 set pcie_aspm [read_file /sys/module/pcie_aspm/parameters/policy]
 if {![string match {*\[performance\]*} $pcie_aspm]} {
 	echo "Warn : Switch PCIe power saving off or the first couple of pulses gets clocked as fast as 20 MHz"
 	echo "Warn : Issue 'echo performance | sudo tee /sys/module/pcie_aspm/parameters/policy'"
 }
 
-set GPIO_CHIP 4
+set GPIO_CHIP [string index [find_rp1_alias] end]
 source [find interface/raspberrypi-gpio-connector.cfg]