ARM: shmobile: dts: Move interrupt-parent property to root node

There's no need to duplicate the interrupt-parent property in all DT
nodes as the kernel automatically walks parent nodes to find the
property. Specify it once in the root node only.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>