omap1: Simplify use of omap_irq_flags

Commit 03a9e512
(omap1: Use asm_irq_flags for entry-macro.S) added support
for multi-omap builds with addition of the omap_irq_flags.

Commit 9f9605c2
(omap2+: Fix unused variable warning for omap_irq_base)
simplified omap2+ entry-macro.S by moving omap_irq_flags
out of entry-macro.S.

Simplify omap1 entry-macro.S in a similar way to keep the
code consistent. Based on a similar earlier patch for omap2+
by Russell King <rmk+kernel@arm.linux.org.uk>.

Signed-off-by: Tony Lindgren <tony@atomide.com>