[ARM] Assembler and disassembler support Dot Product Extension

[ARM] Assembler and disassembler support Dot Product Extension

  This patch add assembler and disassembler support for new Dot Product
  Extension.

  The support can be enabled through the new "+dotprod" extension.

include/
	* opcode/arm.h (FPU_NEON_EXT_DOTPROD): New macro.
	(FPU_ARCH_DOTPROD_NEON_VFP_ARMV8): New macro.

gas/
	* config/tc-arm.c (fpu_neon_ext_dotprod): New variable.
	(neon_scalar_for_mul): Improve comments.
	(do_neon_dotproduct): New function to encode Dot Product instructions.
	(do_neon_dotproduct_s): Wrapper function for signed Dot Product
	instructions.
	(do_neon_dotproduct_u): Wrapper function for unsigned Dot Product
	instructions.
	(insns): New entries for vsdot and vudot.
	(arm_extensions): New entry for "dotprod".
	* doc/c-arm.texi: Document new "dotprod" extension.
	* testsuite/gas/arm/dotprod.s: New test source.
	* testsuite/gas/arm/dotprod-illegal.s: New test source.
	* testsuite/gas/arm/dotprod.d: New test.
	* testsuite/gas/arm/dotprod-thumb2.d: New test.
	* testsuite/gas/arm/dotprod-illegal.d: New test.
	* testsuite/gas/arm/dotprod-legacy-arch.d: New test.
	* testsuite/gas/arm/dotprod-illegal.l: New error file.
	* testsuite/gas/arm/dotprod-legacy-arch.l: New error file.

opcodes/
	* arm-dis.c (coprocessor_opcodes): New entries for vsdot and vudot.

Cherry-pick of c604a79ad4d47070bbcc0bc082188fb16892ceef.

Change-Id: I5521f218ba3627c1f8b3a9ef20277aa02298e2ae