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>

SVN-Revision: 38508

target/linux/ar71xx/nand/target.mk

@@ -1,8 +1,8 @@
-BOARDNAME:=Devices with NAND flash (mostly Mikrotik)
+BOARDNAME:=Mikrotik devices with NAND flash
 
 define Target/Description
-	Build firmware images for Atheros AR71xx/AR913x based boards with 
-	NAND flash, e.g. MikroTik RB-4xx or RB-750
+	Build firmware images for Atheros AR71xx/AR913x based Mikrotik boards.
+	e.g. MikroTik RB-4xx or RB-750
 endef