[ARM][doc] Improve description of AArch32 CRC32 intrinsics.

	* doc/arm-acle-intrinsics.texi: Specify when CRC32 intrinsics are
	available.
	Simplify description of __crc32d and __crc32cd intrinsics.
	* doc/extend.texi (ARM ACLE Intrinsics): Remove comment about CRC32
	availability.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-4_9-branch@211403 138bc75d-0d04-0410-961f-82ee72b054a4
Merge remote-tracking branch 'gnu/gcc-4_9-branch' into linaro-4.9