MIPS: ingenic: Use common cmdline handling code

jz4740_init_cmdline appends all arguments from argv (in fw_arg1) to
arcs_cmdline, up to argc (in fw_arg0). The common code in
fw_init_cmdline will do the exact same thing when run on a system where
fw_arg0 isn't a pointer to kseg0 (it'll also set _fw_envp but we don't
use it). Remove the custom implementation & use the generic code.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Reviewed-by: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Maarten ter Huurne <maarten@treewalker.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18484/


Signed-off-by: James Hogan <jhogan@kernel.org>