ARM: dts: bcm283x: Add Transposer block

The transposer block is allowing one to write the result of the VC4
composition back to memory instead of displaying it on a screen.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Eric Anholt <eric@anholt.net>