[RFC] Dropping Alpha sparse mapping support from X

Hi,
I'd like to drop support for non-BWX Alphas (EV4 and original EV5)
from X. These machines can't load/store to single bytes and require
special sparse memory mappings.

The code required to select which functions (sparse, dense) is
convoluted, adds an extra layer of indirection, probably gets close to
zero usage, and even less testing.

Does anyone use X on EV4 or EV5 (not EV56, EV56 has BWX)?

Thanks,
Matt Turner