[ARM] Don't warn on REG_SP when used in CRC32 instructions

[ARM] Don't warn on REG_SP when used in CRC32 instructions

According to ARMv8-A architecture manual, REG_SP is allowed in CRC32
instructions in Thumb mode.  It is REG_PC that will cause unpredictable
behaviours on both ARM and Thumb.

This patch removes the incorrect warning on Thumb mode.

Meanwhile the disassembler is updated to use format "<bitfield>R" instead of
"<bitfield>S".  "<bitfield>S" is not used elsewhere. so I have deleted related
code from the disassembler.

gas/
	* config/tc-arm.c (do_crc32_1): Remove warning on REG_SP for thumb_mode.
	* testsuite/gas/arm/crc32-armv8-a-bad.d: Update exepcted result.
	* testsuite/gas/arm/crc32-armv8-r-bad.d: Likewise.
	* testsuite/gas/arm/crc32-armv8-a.d: Likewise.
	* testsuite/gas/arm/crc32-armv8-r.d: Likewise.
	* testsuite/gas/arm/crc32-armv8-ar-bad.s: Update test case.
	* testsuite/gas/arm/crc32-armv8-ar.s: Likewise.
	* testsuite/gas/arm/crc32-bad.l: Update expected error message.

opcode/
	* arm-dis.c (thumb32_opcodes): Use format 'R' instead of 'S' for
	register operands in CRC instructions.
	(print_insn_thumb32): Remove "<bitfield>S" support.  Updated the
	comments.