ARM: mach-shmobile: mackerel: update defconfig
* Enable ARM_APPENDED_DTB
Typically the bootloader of a mackerel board does not support DT
so this option is useful
* Add "rw" to command line
This appears to be necessary for a successful NFS-root boot
* Remove memchunk from kernel command line,
it is not used outside of arch/sh
* Move command line to dts
This brings us one small step closer to sharing defconfig
between mackerel and other boards
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>