ar71xx: remove 'Target/Description' from main Makefile

Ensure that menuconfig shows the correct help text for
subtargets.

Based on the patch by Stefan Agner:
http://patchwork.openwrt.org/patch/4123/

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38507 3c298f89-4303-0410-b956-a3cf2f4a3e73
ar71xx: change title and description for NAND subtarget

The nand subtarget supports Mikrotik boards only. Change
the title and the description to reflect that.

Based on the patch by Stefan Agner:
http://patchwork.openwrt.org/patch/4123/

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38508 3c298f89-4303-0410-b956-a3cf2f4a3e73
ar71xx: rename 'nand' subtarget to 'mikrotik'

It is for Mikrotik devices only, rename the subtarget
to reflect that. Also fix the wget2nand script to use
the new image names.

Based on the patch by Stefan Agner:
http://patchwork.openwrt.org/patch/4123/

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38509 3c298f89-4303-0410-b956-a3cf2f4a3e73