[arm] Fix typo in is_simple_expr.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13228 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
[coloring] Validate physical register offsets.

The ARM backend uses several tricks to support selection of
VFP3_D16/VFP3_D32 when ocamlopt is invoked, which introduces
interferences with non-existing floating-point registers when
the VFP3_D16 fpu option is used. These invalid interferences
must be skipped while coloring the graph.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13229 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02