m68k: set appropriate machine type for m5411x SoC platforms

Create a new machine type for platforms based around the ColdFire 5441x
SoC family. Set that machine type on startup when building for this
platform type.

Currently the ColdFire head.S hard codes a M54xx machine type at startup -
since that is the only platform type currently supported with MMU enabled.
The m5441x has an MMU and this change forms part of the support required
to run it with the MMU enabled.

Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>