extra-dts: Move i2c clock frequency dts to package

Rather than commiting the compiled device tree overlays to source
control, this puts the dts files in a custom package and builds them.

The device tree files are currently bit for bit identical. The only
change that I made was to rename them to the standard Linux conventions:
`.dts` for a terminal device tree file (i.e., not an include) and
`.dtbo` for a compiled device tree overlay.

Author: fhunleth

Config.in

@@ -0,0 +1,3 @@
+# Add project-specific packages for Buildroot here
+
+source "$NERVES_DEFCONFIG_DIR/package/extra-dts/Config.in"

README.md

@@ -308,8 +308,8 @@ to. The device tree blob can be found in `/lib/firmware`.
 Choose one of the following:
 
 ```text
-uboot_setenv(uboot-env, "uboot_overlay_addr4", "/lib/firmware/i2c1-clock-frequency-100khz.dtb")
-uboot_setenv(uboot-env, "uboot_overlay_addr5", "/lib/firmware/i2c2-clock-frequency-100khz.dtb")
+uboot_setenv(uboot-env, "uboot_overlay_addr4", "/lib/firmware/i2c1-clock-frequency-100khz.dtbo")
+uboot_setenv(uboot-env, "uboot_overlay_addr5", "/lib/firmware/i2c2-clock-frequency-100khz.dtbo")
 ```
 
 You can configure your project to enable these device tree overlays by copying the

external.mk

@@ -0,0 +1,2 @@
+# Include system-specific packages
+include $(sort $(wildcard $(NERVES_DEFCONFIG_DIR)/package/*/*.mk))

nerves_defconfig

@@ -67,3 +67,4 @@ BR2_NERVES_SYSTEM_NAME="nerves_system_bbb"
 BR2_PACKAGE_BBORG_OVERLAYS=y
 BR2_PACKAGE_NBTTY=y
 BR2_PACKAGE_NERVES_CONFIG=y
+BR2_PACKAGE_EXTRA_DTS=y

package/extra-dts/Config.in

@@ -0,0 +1,5 @@
+menuconfig BR2_PACKAGE_EXTRA_DTS
+	bool "extra-dts"
+	select BR2_PACKAGE_HOST_DTC
+	help
+	  Extra DTS files that may be useful on Nerves systems.

package/extra-dts/extra-dts.mk

@@ -0,0 +1,26 @@
+#############################################################
+#
+# extra-dts
+#
+#############################################################
+
+# Remember to bump the version when anything changes in this
+# directory.
+EXTRA_DTS_SOURCE =
+EXTRA_DTS_VERSION = 0.0.1
+EXTRA_DTS_DEPENDENCIES = host-dtc
+
+define EXTRA_DTS_BUILD_CMDS
+	cp $(NERVES_DEFCONFIG_DIR)/package/extra-dts/*.dts* $(@D)
+        for filename in $(@D)/*.dts; do \
+            $(CPP) -I$(@D) -nostdinc -undef -D__DTS__ -x assembler-with-cpp $$filename | \
+              $(HOST_DIR)/usr/bin/dtc -Wno-unit_address_vs_reg -@ -I dts -O dtb -b 0 -o $${filename%.dts}.dtbo || exit 1; \
+        done
+endef
+
+define EXTRA_DTS_INSTALL_TARGET_CMDS
+        cp $(@D)/*.dtbo $(TARGET_DIR)/lib/firmware
+endef
+
+
+$(eval $(generic-package))