ARM: shmobile: marzen: Remove legacy board code

Remove Marzen legacy board code written in C. Instead
board support expressed in DT shall be used together
with Multiplatform and shmobile_defconfig.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>