kernel/linux: change m68k/no-mmu linux arch tuple to use -uclinux

GCC requires m68k arch tuples to be *-*-uclinux-* to support Linux on
no-mmu m68k (ColdFire) cpus.

Blackfin arch tuple must be *-*-linux-uclibc for FD_PIC_ELF toolchains,
so we cannot just switch to uclinux for no-mmu Linux toolchains.

Signed-off-by: "Esben Haabendal" <esben@haabendal.dk>
Message-Id: <876271s1ee.fsf@arh128.prevas.dk>
PatchWork-Id: 186976

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