[MIPS] MTX-1: Add GPIO system button

This patch adds support for the GPIO connected system button on the MTX-1
boards. Default configuration is updated accordingly.

Signed-off-by: Florian Fainelli <florian.fainelli@telecomint.eu>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2 files changed