ARM: dts: OMAP4: Cleanup and move GIC outside of the OCP

Remove some useless comment and move GIC controller outside
of the OCP node since it does use the MPU internal bus and
not the OCP.
This will not change the functionality but will reflect the
reality more accurately.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>