crypto: powerpc/sha1 - assembler

This is the assembler code for SHA1 implementation with
the SIMD SPE instruction set. With the enhanced instruction
set we can operate on 2 32 bit words in parallel. That helps
reducing the time to calculate W16-W79. For increasing
performance even more the assembler function can compute
hashes for more than one 64 byte input block.

The state of the used SPE registers is preserved via the
stack so we can run from interrupt context. There might
be the case that we interrupt ourselves and push sensitive
data from another context onto our stack. Clear this area
in the stack afterwards to avoid information leakage.

The code is endian independant.
Signed-off-by: Markus Stockhausen <stockhausen@collogia.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>