ARM: S3C6400: Update s3c6400_defconfig for bigger initrds for SMDK6410

The Samsung initrd for SMDK6410 is now bigger than the original initrds
that where used. Increase the command-line size and the size of the ramdisk
that it is unpacked into.

Also change the default init to /linuxrc to avoid problems with the current
SMDK ramdisk image failing to run /bin/bash.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>