MIPS: sead3: remove chosen node

The defaults are not always applicable and it makes it hard for the bootloader
to override them. By removing it we give the bootloader full control over what
command line parameters to pass.

Without this change we will need to modify the built-in dtb to add bootloader
cmd line parameters or do some work to append them after we unflatten the device
tree.

Sead3 is a development board, that's why we want to be able to change boot
parameters on the fly from the bootloader.

Signed-off-by: Qais Yousef <qais.yousef@imgtec.com>
Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6208/