ARM: shmobile: marzen: Do not set command line in defconfig

As a set towards moving shmobile towards multi-platform
the kernel command line should be set in the DTB rather than
in the kernel config.

marzen already has the command line present in its DTS file
but it was being overrirden by the kernel config.

Signed-off-by: Simon Horman <horms@verge.net.au>