Separate common md block code

* cipher/hash-common.c (_gcry_md_block_write): New function to handle
block md operations.  The current implementation is limited to 64 byte
buffer and u32 block counter.
* cipher/md4.c, cipher/md5.c, cipher/rmd.h, cipher/rmd160.c
*cipher/sha1.c, cipher/sha256.c, cipher/tiger.c: Convert to use
_gcry_md_block_write.

Whirlpool and SHA512 are left as before, as SHA512 uses 128 bytes buffer
and u64 blocks counter and Whirlpool does not have trivial block handling
structure.

Indentation changes, minor edits and adjustment of
_gcry_sha1_hash_buffers by wk.

• Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>