lavu/ripemd: Fully unroll the transform function loops

crypto_bench RIPEMD-160 results using an AMD Athlon X2 7750+, mingw32-w64 GCC 4.8.1 x86_64

Before:
lavu       RIPEMD-160   size: 1048576  runs:   1024  time:   12.342 +- 0.199

After:
lavu       RIPEMD-160   size: 1048576  runs:   1024  time:   10.143 +- 0.192

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavu/ripemd: Add a size optimized version of the transform functions

When compiling with --enable-small, ripemd.o will weigh a few kilobytes less than
it used to before the previous commit.

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>