MSM8916/39 do not need signed GPU firmware so it is generally okay to
have it enabled by default. However, currently the GPU does not work
without also enabling MDSS and it's questionable if someone would
really need it without a display in practice.
For consistency let's follow newer SoCs and disable the GPU by default.
Enable it for all existing devices that already have &mdss enabled.
Signed-off-by: Stephan Gerhold <stephan@xxxxxxxxxxx>