x86: Re-enable PCAT timer 2 for beeping

x86: Re-enable PCAT timer 2 for beeping

While we don't want PCAT timers for timing, we want timer 2 so that we can
still make a beep. Re-purpose the PCAT driver for this, and enable it in
coreboot.

Signed-off-by: Simon Glass <sjg@chromium.org>