MIPS: BCM47XX: Use standard reset button for Luxul XWR-1750

MIPS: BCM47XX: Use standard reset button for Luxul XWR-1750

The original patch submitted for support of the Luxul XWR-1750 used a
non-standard button handler for the reset button. This patch will allow
using the standard KEY_RESTART

Signed-off-by: Dan Haab <dan.haab@luxul.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18981/
Signed-off-by: James Hogan <jhogan@kernel.org>