imx: introduce 'cortexa7' subtarget

This adds some essential files required by new 'cortexa7' subtarget,
dedicated for Cortex-A7 based NXP i.MX series. For now, the kernel
config-default focuses only on the i.MX 6UL family, as the following
changeset will introduce support for i.MX 6ULL based device. Support
for more platforms (e.g. i.MX 7) might be enabled later, while adding
more devices.

Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>

target/linux/imx/cortexa7/base-files/etc/board.d/02_network

@@ -0,0 +1,15 @@
+. /lib/functions/uci-defaults.sh
+
+board=$(board_name)
+
+board_config_update
+
+case "$board" in
+*)
+	ucidef_set_interfaces_lan_wan "eth0" "eth1"
+	;;
+esac
+
+board_config_flush
+
+exit 0

target/linux/imx/cortexa7/base-files/lib/upgrade/platform.sh

@@ -0,0 +1,16 @@
+PART_NAME=firmware
+REQUIRE_IMAGE_METADATA=1
+
+platform_check_image() {
+	return 0
+}
+
+platform_do_upgrade() {
+	local board=$(board_name)
+
+	case "$board" in
+	*)
+		default_do_upgrade "$1"
+		;;
+	esac
+}