Update the marzen board to use the INTC External IRQ pin driver for SMSC.

This code was originally posted by Magnus Damm as part of
"ARM: shmobile: INTC External IRQ pin driver on r8a7779"
but somehow omitted when I applied that patch.

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