MIPS: AR7: use ar7_has_high_vlynq() to determine watchdog base address

Instead of doing yet another switch/case on the chip_id, use existing
inline function to set the watchdog base address.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/1211/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>