MIPS: AR7: Initialize GPIO earlier

In order to detect the Titan variant, we must initialize GPIOs earlier since
detection relies on some GPIO values to be set.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/1562/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
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