imx6: rename target to 'imx'

This is first step in migrating to a generic i.MX target which in the
next steps will also get divided into arch-specific subtargets.

In the result, this will make it possible to support, within a single
target, also other modern NXP i.MX families, like the i.MX 7, i.MX 8
or recently introduced i.MX 9.

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

target/linux/imx/Makefile

@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Copyright (C) 2013-2014 OpenWrt.org
+
+include $(TOPDIR)/rules.mk
+
+ARCH:=arm
+BOARD:=imx
+BOARDNAME:=NXP i.MX
+FEATURES:=audio display fpu gpio pcie rtc usb usbgadget squashfs targz nand ubifs boot-part rootfs-part
+CPU_TYPE:=cortex-a9
+CPU_SUBTYPE:=neon
+
+KERNEL_PATCHVER:=5.4
+KERNEL_TESTING_PATCHVER:=5.10
+
+include $(INCLUDE_DIR)/target.mk
+
+KERNELNAME:=zImage dtbs
+
+DEFAULT_PACKAGES += uboot-envtools mkf2fs e2fsprogs blkid
+
+$(eval $(call BuildTarget))