ARM: shmobile: No need to use INTC header on r8a7779

Now when the intc-irqpin driver is used for external
IRQ pins on r8a7779 it possible to get rid of unused
INTC headers mach/intc.h and linux/sh_intc.h.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>