powerpc/pseries: relocate "config DTL" so kconfig nests properly

Moving config DTL up so it is below config PPC_SPLPAR means that
menuconfig will show config DTL nicely indented right below config
PPC_SPLPAR when PPC_SPLPAR is enabled.

To contrast that, right now if I enable PPC_SPLPAR in menuconfig, all I
can immediately tell is that "something showed up further down the list
where I wasn't looking", and I end up having to toggle the option a few
times to figure out what showed up, or look at the KConfig to find out
that config DTL depends on config PPC_SPLPAR.

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>