md5/shaXsum: use FEATURE_COPYBUF_KB to size the buffer instead of fixed 4k

function                                             old     new   delta
md5_sha1_sum_main                                    536     565     +29
hash_file                                            419     401     -18
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 29/-18)             Total: 11 bytes

In my test, for unrolled sha1, COPYBUF_KB=64 increases throughput
from 367 MB/s to 457 MB/s.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
1 file changed