ARM: rmobile: Update M2 Koelsch

The M2 Koelsch port was broken since some time. This patch updates
the M2 Koelsch port to use modern frameworks, DM, DT probing, SPL
for the preloading and puts it on par with the M2 Porter board.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>