msm: irq: Allow 8910 and 8226 IRQ definitions to coexist

Refactor irqs.h to allow irqs-8910.h and irqs-8226.h to be
included together in preparation for single-binary support
for these targets.

Change-Id: Ibb585410d54ae396872b870b0ab6b197d068a652
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>