CRIS: Restore mistakenly cleared kernel Makefile

Commit 0fbc0b67

 ("cris: remove arch specific early DT functions")
was a bit overzealous in removing the CRIS DT handling,
and the complete contents of the Makefile was erased
instead of just the line for the devicetree file.

This lead to a complete link failure for all SoCs in
the CRIS port due to missing symbols.

Restore the contents except the line for the devicetree file.

Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>
Fixes: 0fbc0b67