gpioevents: add support for pull-down and floating input pins.

The pin-mode (ft, pd, pu for floating, pull-down, pull-up) is
specified after the intr-config (no, eb, ef, er) for each pin.

Tested on my Raspberry Pi 1B.

PR: 268504
Approved by: manu
MFC after: 1 week

(cherry picked from commit 453db42291a3179a51b9bf41ca7dbc0a5298bffa)

gpioevents: fix some white-space errors

Fixes: 453db42291a3 - gpioevents: add support for pull-down and floating input pins.
Approved by: manu (implicit)
MFC after: 1 week

(cherry picked from commit e2f3742ab8b10ba5ec4dc190c5b64e9151bb0d57)