brcm2708: restore UART on RPi 0W, 3B, 3B+ and 4B

Disable Bluetooth and restore UART to GPIOs 14 & 15.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

target/linux/brcm2708/image/Makefile

@@ -28,6 +28,7 @@ define Build/boot-common
 	mcopy -i $@.boot $(KDIR)/LICENCE.broadcom ::
 	mcopy -i $@.boot cmdline.txt ::
 	mcopy -i $@.boot $(BOOT_CONFIG) ::config.txt
+	mcopy -i $@.boot distroconfig.txt ::
 	mcopy -i $@.boot $(IMAGE_KERNEL) ::$(KERNEL_IMG)
 	$(foreach dts,$(shell echo $(DEVICE_DTS)),mcopy -i $@.boot $(DTS_DIR)/$(dts).dtb ::;)
 	mmd -i $@.boot ::/overlays

target/linux/brcm2708/image/config-bcm2711-arm64.txt

@@ -9,3 +9,9 @@
 
 # Force aarch64
 arm_64bit=1
+
+# OpenWrt config
+include distroconfig.txt
+
+[all]
+# Place your custom settings here.

target/linux/brcm2708/image/config.txt

@@ -6,3 +6,9 @@
 # For overclocking and various other settings, see:
 # https://www.raspberrypi.org/documentation/configuration/config-txt/README.md
 ################################################################################
+
+# OpenWrt config
+include distroconfig.txt
+
+[all]
+# Place your custom settings here.

target/linux/brcm2708/image/distroconfig.txt

@@ -0,0 +1,14 @@
+################################################################################
+# Bootloader configuration - distroconfig.txt
+################################################################################
+
+# Restore PL011 (ttyAMA0) to GPIOs 14 & 15, instead of Mini UART (ttyS0).
+# Mini UART is disabled by default unless "enable_uart=1" is specified,
+#  which changes the core frequency to a fixed value and impacts performance.
+# See https://www.raspberrypi.org/documentation/configuration/uart.md
+[pi0w]
+dtoverlay=disable-bt
+[pi3]
+dtoverlay=disable-bt
+[pi4]
+dtoverlay=disable-bt