xtensa: Make full transition to LRA

xtensa: Make full transition to LRA

gcc/ChangeLog:

	* config/xtensa/constraints.md (R, T, U):
	Change define_constraint to define_memory_constraint.
	* config/xtensa/predicates.md (move_operand): Don't check that a
	constant pool operand size is a multiple of UNITS_PER_WORD.
	* config/xtensa/xtensa.cc
	(xtensa_lra_p, TARGET_LRA_P): Remove.
	(xtensa_emit_move_sequence): Remove "if (reload_in_progress)"
	clause as it can no longer be true.
	(fixup_subreg_mem): Drop function.
	(xtensa_output_integer_literal_parts): Consider 16-bit wide
	constants.
	(xtensa_legitimate_constant_p): Add short-circuit path for
	integer load instructions. Don't check that mode size is
	at least UNITS_PER_WORD.
	* config/xtensa/xtensa.md (movsf): Use can_create_pseudo_p()
	rather reload_in_progress and reload_completed.
	(doloop_end): Drop operand 2.
	(movhi_internal): Add alternative loading constant from a
	literal pool.
	(define_split for DI register_operand): Don't limit to
	!TARGET_AUTO_LITPOOLS.
	* config/xtensa/xtensa.opt (mlra): Change to no effect.