Replace interleave_size with channel_hash

Replace interleave_size with channel_hash

This patch replaces the previously introduced interleave_size memory
channel decoding mechanism with a more powerful channel_hash. Decoding
can now be based upon an arbitrary mask of address bits, which will be
XORed together to determine the target channel. Note that this drops
support for more than two channels, but TripleChannel controllers will
probably use much more complicated decoding mechanisms anyway.

It also includes the findmask program, which offers a crude method to
guess the decoding mask from an unknown memory controller for enterprising
users. Use at your own risk.

Signed-off-by: Julius Werner <jwerner@chromium.org>