MIPS: BCM63xx: Avoid namespace clash on GPIO_DIR_{IN,OUT}

This is too generic a name, so prefix it with BCM63XX_ to avoid potential
namespace clashes when including <asm/gpio.h>.

Signed-off-by: Florian Fainelli <ffainelli@freebox.fr>
To:     linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/1171/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>