Allow non-root access to GPIO & PWM sysfs nodes

Mechanism borrowed from Pi to ensure full compatibility with libs
like python-periphery.
https://github.com/RPi-Distro/raspberrypi-sys-mods/blob/master/etc.armhf/udev/rules.d/99-com.rules

Note that a separate group 'gpio' is not used, instead the existing
group 'input' is. This is to allow updating an already flashed board
with this package to get the feature without re-flashing. Pi adds
the gpio group at image build time, requiring re-flash or manual
groupadd after update.

BUG: 144068132
Change-Id: I27ad8f826536ad6461496a6891c486311e8104d7