Revert PCIe Gen 3 config: restore safe defaults for public image

The PCIe Gen 3 changes (dtparam=pciex1_gen=3, full configTxt
replacement, SBC overlay upgrade fix) caused boot failures during
talosctl upgrade on CM5 nodes. Revert to the pre-Gen3 state:
- configTxtAppend (overclock only) instead of full configTxt replacement
- Remove 0003 overlay patch application (kept in patches/ for future use)

PCIe Gen 3 support will be re-added after root cause analysis.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Makefile

@@ -57,7 +57,7 @@ ATTESTATION_ARGS = --provenance=mode=max --sbom=true
 IMAGER_COMMON_FLAGS = \
 	--overlay-name="rpi5" \
 	--overlay-image="$(OVERLAY_IMAGE):$(SBCOVERLAY_TAG)" \
-	--overlay-option="configTxt=$$(cat $(PWD)/config/config.txt)" \
+	--overlay-option="configTxtAppend=$$(cat $(PWD)/config/config.txt.append)" \
 	$(EXTENSION_FLAGS)
 
 #
@@ -124,8 +124,7 @@ patches-overlay:
 		else \
 			echo "Overlay Go $$GO_VER — skipping Go toolchain patch (CVEs fixed upstream)"; \
 		fi && \
-		git am "$(PATCHES_DIRECTORY)/talos-rpi5/sbc-raspberrypi5/0002-"*.patch && \
+		git am "$(PATCHES_DIRECTORY)/talos-rpi5/sbc-raspberrypi5/0002-"*.patch
-		git am "$(PATCHES_DIRECTORY)/talos-rpi5/sbc-raspberrypi5/0003-"*.patch
 
 patches: patches-pkgs patches-talos patches-overlay
 

config/config.txt

@@ -1,30 +0,0 @@
-# See https://www.raspberrypi.com/documentation/computers/configuration.html
-# Reduce GPU memory to give more to CPU.
-gpu_mem=32
-# Enable maximum compatibility on both HDMI ports;
-# only the one closest to the power/USB-C port will work in practice.
-hdmi_safe:0=1
-hdmi_safe:1=1
-# Load U-Boot.
-kernel=u-boot.bin
-# Forces the kernel loading system to assume a 64-bit kernel.
-arm_64bit=1
-# Run as fast as firmware / board allows.
-arm_boost=1
-# Enable the primary/console UART (globally).
-enable_uart=1
-# Disable UART on Pi5 to avoid U-Boot compatibility issue.
-# The debug UART (ttyAMA10) is always active regardless of this setting.
-[pi5]
-enable_uart=0
-# Enable PCIe Gen 3 for NVMe (~800 MB/s vs ~400 MB/s Gen 2)
-dtparam=pciex1_gen=3
-[all]
-# Disable Bluetooth.
-dtoverlay=disable-bt
-# Disable Wireless Lan.
-dtoverlay=disable-wifi
-# CM5 Overclock — 2.6GHz stable on Compute Blade with heatsink
-arm_freq=2600
-over_voltage_delta=50000
-arm_boost=1