ARM: highbank: select SPARSE_IRQ and remove irqs.h

irqs.h is optional now for SPARSE_IRQ, so select it and remove mach/irqs.h
from highbank.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 30e7840..dcd77db 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -349,6 +349,7 @@
 	select GENERIC_CLOCKEVENTS
 	select HAVE_ARM_SCU
 	select HAVE_SMP
+	select SPARSE_IRQ
 	select USE_OF
 	help
 	  Support for the Calxeda Highbank SoC based boards.