MIPS: arc: use function argument for passing argc/argv to prom_init_cmdline

MIPS: arc: use function argument for passing argc/argv to prom_init_cmdline

prom_argc and prom_argv are only used by prom_init_cmdline(), so
we could pass them directly as function argument.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org