arm: Enable no-writeback vldr.16/vstr.16.

arm: Enable no-writeback vldr.16/vstr.16.

There was previously no way to specify that a register operand cannot
have any writeback modifiers, and as a result the argument to vldr.16
and vstr.16 could be erroneously output with post-increment. This
change adds a constraint which forbids all writeback, and
selects it in the relevant case for vldr.16 and vstr.16

Bootstrapped on arm-linux, gcc and CMSIS-DSP testsuites are clean.
Is this patch OK for trunk? If yes, please commit on my behalf as I
don't
have commit rights.

gcc/ChangeLog:

	* config/arm/arm-protos.h (arm_coproc_mem_operand_no_writeback):
	Declare prototype.
	(arm_mve_mode_and_operands_type_check): Declare prototype.
	* config/arm/arm.c (arm_coproc_mem_operand): Refactor to use
	_arm_coproc_mem_operand.
	(arm_coproc_mem_operand_wb): New function to cover full, limited
	and no writeback.
	(arm_coproc_mem_operand_no_writeback): New constraint for memory
	operand with no writeback.
	(arm_print_operand): Extend 'E' specifier for memory operand
	that does not support writeback.
	(arm_mve_mode_and_operands_type_check): New constraint check for
	MVE memory operands.
	* config/arm/constraints.md: Add Uj constraint for VFP vldr.16
	and vstr.16.
	* config/arm/vfp.md (*mov_load_vfp_hf16): New pattern for
	vldr.16.
	(*mov_store_vfp_hf16): New pattern for vstr.16.
	(*mov<mode>_vfp_<mode>16): Remove MVE moves.