shift.md: Rewrite...

* config/m32c/shift.md: Rewrite: Allow arbitrary operands for
shift counts, separate SI shifts for m32c vs m16c, pass shift type
so that constant shifts can be split.
* config/m32c/m32c.c (m32c_const_ok_for_constraint_p): Add In6.
(m32c_valid_pointer_mode): Make static.
(shift_gen_func_for): New.
(m32c_prepare_shift): Use it.  Split large const shifts into
multiple shifts.
* config/m32c/predicates.md (shiftcount_operand): Allow more
general operands.
(longshiftcount_operand): New.
* doc/md.texi (Machine Constraints): Document In6.

From-SVN: r109661