mox-support: Add shield support and split package

Split package into various subpackages, mainly to have versioning correct - only dtb is version by kernel version, rest don't need to be updated all the time. To add shield support package that contains only shield specific stuff I also split out generic MOX stuff like button handling and nor content into separate package.

hardware/mox/mox-dtb/Makefile

+#
+## Copyright (C) 2020 CZ.NIC z.s.p.o. (https://www.nic.cz/)
+#
+## This is free software, licensed under the GNU General Public License v3.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+include $(INCLUDE_DIR)/kernel.mk
+
+PKG_NAME:=mox-dtb
+PKG_VERSION:=$(LINUX_VERSION)-$(LINUX_RELEASE)-$(LINUX_VERMAGIC)
+PKG_RELEASE:=1
+PKG_MAINTAINER:=CZ.NIC <packaging@turris.cz>
+PKG_BUILD_DIR:=$(KERNEL_BUILD_DIR)/packages
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/mox-dtb
+  TITLE:=Device tree for Turris MOX
+  DEPENDS:=@TARGET_mvebu_cortexa53_DEVICE_cznic-mox
+endef
+
+define Package/mox-dtb/description
+ Contains device tree for Turris MOX.
+endef
+
+define Build/Prepare
+	mkdir -p $(PKG_BUILD_DIR)
+endef
+
+define Build/Compile
+	$(KERNEL_MAKE) Image dtbs
+endef
+
+define Package/mox-dtb/install
+	$(INSTALL_DIR) $(1)/boot
+	$(CP) $(LINUX_DIR)/arch/$(LINUX_KARCH)/boot/dts/marvell/armada-3720-turris-mox.dtb "$(1)"/boot
+endef
+
+$(eval $(call BuildPackage,mox-dtb))