ARM: dts: Configure am3 and am4 sgx for genpd and drop platform data

We can power off the SGX power domain when not in use when we configure
it for genpd. And with that change, we can now also drop the old unused
legacy platform data.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>