ARM: dts: Add missing hsi node for omap4

On omap4 we're missing the hsi node with it's related "ti,hwmods"
property that the SoC interconnect code needs.

Note that this will only show up as a bug with "doesn't have
mpu register target base" boot errors when the legacy platform
data is removed.

Let's also update the binding accrodingly while at it.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Rob Herring <robh+dt@kernel.org>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>