[RISCV] Initial codegen support for the XRivosVizip extension (#131933)

This implements initial code generation support for a subset of the
xrivosvizip extension. Specifically, this adds support for vzipeven,
vzipodd, and vzip2a, but not vzip2b, vunzip2a, or vunzip2b. The others
will follow in separate patches.

One review note: The zipeven/zipodd matchers were recently rewritten to
better match upstream style, so careful review there would be
appreciated. The matchers don't yet support type coercion to wider
types. This will be done in a future patch.

0 files changed, 0 insertions, 0 deletions