The original way we determined the gpu version was based on downstream
bindings from android kernel.  A cleaner way is to get the version from
the compatible string.

Note that no upstream dtb uses these bindings.  But the code still
supports falling back to the legacy bindings (with a warning), so that
we are still compatible with the gpu dt node from android device
kernels.
Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Rob Herring <robh@kernel.org>