arm: imx: remove bmode , hdmidet and dek commands from SPL

These files are blowing up the SPL and should not be required
there as the SPL delivers no command console. Because building fails
for mx27 and mx31 machines with SPL build, we remove the linker flag
for them from the Makefile. Nothing is built for them to be linked
in that directory.

Cc: sbabic@denx.de

v2 Changes:
 - Remove mx27 and mx31 from Makefile during SPL build as nothing is built for
   them in that directory. And removing the commands with the libs-y directive
   lead to linker failures. e.g. "armv5te-ld.bfd: cannot find arch/arm/imx-common/built-in.o: No such file or directory)"

Signed-off-by: Sven Ebenfeld <sven.ebenfeld@gmail.com>
Reviewed-by: George McCollister <george.mccollister@gmail.com>
Tested-by: George McCollister <george.mccollister@gmail.com>