ablk_*_init functions share more common code than what is currently in
ablk_init_common. Move all of the common code to ablk_init_common.

Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: NJussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>