md5_file() uses a mmap() window to improve performance when hashing files, so
refactor the code and do the same for SHA1 and SHA256.
(Bitbake rev: ecf87437ff796e17c3e4f210b5803b0136a9e8a4)
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>