crypto: nx - make platform drivers directly register with crypto

Remove the common 'platform' registration module, and move the crypto
compression driver registration into each of the pSeries and PowerNV
platform NX 842 drivers.  Change the nx-842.c code into simple common
functions that each platform driver uses to perform constraints-based
buffer changes, i.e. realigning and/or resizing buffers to match the
driver's hardware requirements.

The common 'platform' module was my mistake to create - since each
platform driver will only load/operate when running on its own
platform (i.e. a pSeries platform or a PowerNV platform), they can
directly register with the crypto subsystem, using the same alg and
driver name.  This removes unneeded complexity.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>