Thanks all. Created a local patch and was able to boot via uboot commands. Someone more knowledgeable might be able to add config vars to this patch to make it respect the settings chosen in kernel_menuconfig.
--- a/arch/mips/ralink/of.c
+++ b/arch/mips/ralink/of.c
@@ -98,10 +98,6 @@ void __init plat_mem_setup(void)
__dt_setup_arch(&__image_dtb);
of_scan_flat_dt(early_init_dt_find_chosen, NULL);
- if (chosen_dtb)
- strlcpy(arcs_cmdline, boot_command_line, COMMAND_LINE_SIZE);
-
- strlcpy(arcs_cmdline, boot_command_line, COMMAND_LINE_SIZE);
of_scan_flat_dt(early_init_dt_find_memory, NULL);
if (memory_dtb)