kernel: other.mk: add pps-gpio support

The pps-gpio kernel module supports Pulse-Per-Second provided by a GPIO.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@40831 3c298f89-4303-0410-b956-a3cf2f4a3e73