arm: omap: irq: add specific compatibles for omap3 and am33xx devices

with this, we can use a compatible flag to figure
out how many irq lines are wired up, no need for
our TI-specific ti,intc-size binding.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>