[AArch64] Accept more addressing modes for PRFM

[AArch64] Accept more addressing modes for PRFM

	* config/aarch64/aarch64.md (prefetch); Adjust predicate and
	constraint on operand 0 to allow more general addressing modes.
	Adjust output template.
	* config/aarch64/aarch64.c (aarch64_address_valid_for_prefetch_p):
	New function.
	* config/aarch64/aarch64-protos.h
	(aarch64_address_valid_for_prefetch_p): Declare prototype.
	* config/aarch64/constraints.md (Dp): New address constraint.
	* config/aarch64/predicates.md (aarch64_prefetch_operand): New
	predicate.

	* gcc.target/aarch64/prfm_imm_offset_1.c: New test.

From-SVN: r247603