soc: ti: omap-prm: Configure sgx power domain for am3 and am4

Let's configure only sgx power domain for am3 and am4 to start with.

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