staging: android: ion: Rework heap registration/enumeration

The current model of Ion heap registration  is based on the outdated
model of board files. The replacement for board files (devicetree)
isn't a good replacement for what Ion wants to do. In actuality, Ion
wants to show what memory is available in the system for something else
to figure out what to use. Switch to a model where Ion creates its
device unconditionally and heaps are registed as available regions.
Currently, only system and CMA heaps are converted over to the new
model. Carveout and chunk heaps can be converted over when someone wants
to figure out how.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>