m68knommu: put ColdFire head code into .text.head section

Switch the ColdFire head start up code to be in the .text.head segment.
And make sure that segment is at the start of the final linked text
segment. Fixes the linker warnings about section use mis-matches:

  WARNING: vmlinux.o(.text+0xa8): Section mismatch in reference from the variable _clear_bss to the function .init.text:start_kernel()
  The function _clear_bss() references
  the function __init start_kernel().
  This is often because _clear_bss lacks a __init
  annotation or the annotation of start_kernel is wrong.

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