ARM: SIRF: make sirf irqchip driver optional since new SoCs will have GIC

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: Barry Song <Baohua.Song@csr.com>
diff --git a/arch/arm/mach-prima2/Kconfig b/arch/arm/mach-prima2/Kconfig
index 65438e1..41fc853 100644
--- a/arch/arm/mach-prima2/Kconfig
+++ b/arch/arm/mach-prima2/Kconfig
@@ -7,9 +7,13 @@
 	default y
 	select CPU_V7
 	select ZONE_DMA
+	select SIRF_IRQ
 	help
           Support for CSR SiRFSoC ARM Cortex A9 Platform
 
 endmenu
 
+config SIRF_IRQ
+	bool
+
 endif