[media] ati_remote: Better default keycodes

This tries to make them more like other remotes, and/or
the button labels.

Notably, the (>>) button is made KEY_FASTFORWARD, which is the
correct opposite of (<<)'s KEY_REVERSE.  (It was KEY_FORWARD,
something else entirely.)

Likewise, KEY_STOP is the Sun keyboard "interrupt program" key;
the media key is KEY_STOPCD.

A restriction is that I try to avoid keycodes above 255, as the X11
client/server protocol is limited to 8-bit key codes.  If not for
this, I would have used the KEY_NUMERIC_x codes for the numbers.

Signed-off-by: George Spelvin <linux@horizon.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>