ARC Linux by default checks for uboot provided args as pointers to
external cmdline or DTB. This however breaks in absence of uboot,
when booting from Metaware debugger directly, as the registers are
not zeroed out on reset by mdb and/or ARCv2 based cores. The bogus
registers look like uboot args to kernel which then chokes.
So only enable the uboot arg checking/processing if users are sure
of uboot being in play.