AArch64: Detect crc32 extension support from assembler

AArch64: Detect crc32 extension support from assembler

The used compiler may or may not be recent enough to recognize the
crc32 extended cpu type. However, it does not really have to know about
them either, since all we do is pass inline assembly instructions to
the assembler.

This patch moves the crc cpu extension detection from compiler based
to assembler based, so that we can build optimized code even when the
compiler does not know about the cpu type yet.

Fixes: http://tracker.ceph.com/issues/17516
Signed-off-by: Alexander Graf <agraf@suse.de>