MIPS: PowerTV: Simplify command line handling and needed config changes

Additional changes to Youichi Yuasa's command line simplication code

The PowerTV platform uses a non-standard way to get the kernel command
line--we insert a built-in command line into arcs_cmdline and to
get additional command line information from the bootloader via a
pointer in the a1 register. It is necessary to insert a space between
to the two strings or the last argument from arcs_cmdline and the first
argument from the bootloader may be inadvertantly combined.

It is also necessary to set CONFIG_CMDLINE_BOOL to "y" and to set the
default command line to an empty string to get the simplified code to
work properly in the PowerTV environment.

Signed-off-by: David VomLehn <dvomlehn@cisco.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1438/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>