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/image/recovery-toradex_apalis

@@ -0,0 +1,15 @@
+# flash u-boot-with-spl.imx
+# using fixed size of 1M for U-Boot + SPL
+mmc dev 0 1
+mmc write 0x12100000 0x2 0x800
+
+# flash openwrt-imx6-apalis-squashfs.combined.bin
+setenv set_blkcnt 'setexpr blkcnt ${filesize} + 0x1ff && setexpr blkcnt ${blkcnt} / 0x200'
+run set_blkcnt
+mmc dev 0 0
+mmc write 0x12500000 0 ${blkcnt}
+
+env default -f -a
+saveenv
+
+reset