brcm47xx: update legacy subtarget description

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45310 3c298f89-4303-0410-b956-a3cf2f4a3e73

target/linux/brcm47xx/legacy/target.mk

 FEATURES += low_mem pcmcia
-BOARDNAME:=Legacy (802.11g)
+BOARDNAME:=Legacy (BMIPS3300)
 
 define Target/Description
-	Build generic firmware for legacy 802.11g Broadcom BCM47xx
-	and BCM53xx MIPS devices.
+	Build firmware for Broadcom BCM47xx and BCM53xx devices with
+	BMIPS3300 CPU except for BCM4705 SoC.
+	Supported SoCs: BCM5352E, BCM5354, BCM5365?, BCM4712, BCM4704.
 endef