compressor: move QatAccel out of common

compressor: move QatAccel out of common

move the QatAccel instance out of the Compressor base class and into
the zlib and lz4 compressors that can use it

this avoids having to link QAT into the ceph-common library, and only
the plugins where it's necessary

had to add LZ4Compressor.cc to store the new static variable

Signed-off-by: Casey Bodley <cbodley@redhat.com>