ARM: dts: OMAP: Move interrupt-parent to the root node to avoid duplication

The interrupt-parent attribute does not have to be added in each
node since the fmwk will check for the parent as well to get it.

Create an interrupt-parent for OMAP2, OMAP3, AM33xx and remove the
attributes from every nodes that were using it.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Cc: Vaibhav Hiremath <hvaibhav@ti.com>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: Sebastien Guiriec <s-guiriec@ti.com>