ARM: shmobile: Remove Marzen from shmobile_defconfig

Kill of the defconfig bits now when the marzen-reference board code is gone.

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>