Simplify config: use configTxtAppend, drop SBC overlay patch

Config.txt is set correctly at flash time. Upgrades via talosctl
don't override firmware config (overlay writes to wrong path on
SBC layout, which is harmless). Users who need custom config.txt
set it once during initial flash.

- Use configTxtAppend with PCIe Gen 3 + overclock
- Put dtparam=pciex1_gen=3 in [pi5] section
- Remove patch 0003 (SBC overlay upgrade fix) — too risky,
  deleted GRUB's BOOTAA64.EFI in v8
- Remove full configTxt replacement mode

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

config/config.txt.append

@@ -1,8 +1,8 @@
+# Enable PCIe Gen 3 for NVMe (~800 MB/s vs ~400 MB/s Gen 2)
+[pi5]
+dtparam=pciex1_gen=3
+[all]
 # CM5 Overclock — 2.6GHz stable on Compute Blade with heatsink
 arm_freq=2600
 over_voltage_delta=50000
 arm_boost=1
-
-# Enable external PCIe link and set Gen 3 for NVMe (~800 MB/s vs ~400 MB/s Gen 2)
-dtparam=pciex1
-dtparam=pciex1_gen=3