bus: ti-sysc: Make omap3 gpt12 quirk handling SoC specific

On beagleboard revisions A to B4 we need to use gpt12 as the system timer.
However, the quirk handling added for gpt12 caused a regression for system
suspend for am335x as the PM coprocessor needs the timers idled for
suspend.

Let's make the gpt12 quirk specific to omap34xx, other SoCs don't need
it. Beagleboard revisions C and later no longer need to use the gpt12
related quirk. Then at some point, if we decide to drop support for the old
beagleboard revisions A to B4, we can also drop the gpt12 related quirks
completely.

Fixes: 3ff340e2

 ("bus: ti-sysc: Fix gpt12 system timer issue with reserved status")
Reported-by: Kevin Hilman <khilman@baylibre.com>
Suggested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>