On am33xx we're missing the pmu and emif nodes with their related
"ti,hwmods" properties 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 related binding documentation while at it.

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