omap2/3/4: Clean up defines for entry-macro.S

Define the irq base the same way as for omap2 and omap3,
and start using get_irqnr_preamble.

Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>