make mcore use constraints.md
	* config/mcore/constraints.md: New file.
	* config/mcore/mcore.md: Include it.
	* config/mcore/mcore.c (reg_class_from_letter): Delete.
	* config/mcore/mcore.h (reg_class_from_letter): Delete.
	(REG_CLASS_FROM_LETTER): Delete.
	(CONST_OK_FOR_I, CONST_OK_FOR_J, CONST_OK_FOR_L): Use
	insn_const_int_ok_for_constraint.
	(CONST_OK_FOR_K, CONST_OK_FOR_M, CONST_OK_FOR_N): Likewise.
	(CONST_OK_FOR_O, CONST_OK_FOR_P): Likewise.
	(CONST_OK_FOR_LETTER_P, CONST_DOUBLE_OK_FOR_LETTER_P): Delete.
	(EXTRA_CONSTRAINT): Delete.

From-SVN: r170134