soc: renesas: rcar-sysc: Merge PM Domain registration and linking

Commit 977d5ba4

 ("soc: renesas: rcar-sysc: Make PM domain
initialization more robust") split PM Domain registration and the
linking of children to their parents, to accommodate PM Domain tables
that list child domains before their parents.

However, this failed to realize that parent power domains must be
powered up before their children anyway, and that this thus must be
reflected by the order in the PM Domain tables.

Revert the split, as it did not help anyway.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>