Add to the AArch64 GAS the missing support for hexadecimal-format

Add to the AArch64 GAS the missing support for hexadecimal-format
floating-point literal in the FMOV instruction.

gas/

	* config/tc-aarch64.c (aarch64_imm_float_p): Rename 'e' to 'pattern';
	add comment.
	(aarch64_double_precision_fmovable): New function.
	(parse_aarch64_imm_float): Add parameter 'dp_p'; call the new
	function; handle hexadecimal representation of IEEE754 encoding.
	(parse_operands): Update the call to parse_aarch64_imm_float.

gas/testsuite/

	* gas/aarch64/diagnostic.s: Add test.
	* gas/aarch64/diagnostic.l: Update.
	* gas/aarch64/illegal.s: Add test.
	* gas/aarch64/illegal.l: Update.
	* gas/aarch64/fpmov.s: New file.
	* gas/aarch64/fpmov.d: New file.