The basic scheme of the block mode assembler is that we start by
enabling the FPU, loading the key into the floating point registers,
then iterate calling the encrypt/decrypt routine for each block.

For the 256-bit key cases, we run short on registers in the unrolled
loops.

So the {ENCRYPT,DECRYPT}_256_2() macros reload the key registers that
get clobbered.

The unrolled macros, {ENCRYPT,DECRYPT}_256(), are not mindful of this.

So if we have a mix of multi-block and single-block calls, the
single-block unrolled 256-bit encrypt/decrypt can run with some
of the key registers clobbered.

Handle this by always explicitly loading those registers before using
the non-unrolled 256-bit macro.

This was discovered thanks to all of the new test cases added by
Jussi Kivilinna.
Signed-off-by: David S. Miller <davem@davemloft.net>