New MARCO and POLO SoC use GIC, so make irq.c optional and enable it
only if we enable ARCH_PRIMA2 in Kconfig
Signed-off-by: NBarry Song <Baohua.Song@csr.com>

Now we have primaII, but will include Marco and Polo in mach-prima2
as well. We add Kconfig menu so that we can select necessary SoC
features.
Signed-off-by: NBarry Song <Baohua.Song@csr.com>