ARM: shmobile: sh73a0 dtsi: Move interrupt-parent to the top

Add an "interrupt-parent = <&gic>;" at the top, which is inherited by
all child nodes, so the "interrupt-parent" properties can be removed
from the individual child nodes.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>