zink: Add mapping for nir_op_ldexp, but disable it for 64-bit's sake.

zink: Add mapping for nir_op_ldexp, but disable it for 64-bit's sake.

We previously had GLSL do ldexp lowering to bitops, but NIR can do it
instead.  It's tempting to just pass the NIR op through to the host Vulkan
driver, but to do that we'd need to split up NIR's flag between 32 and
64-bit support, and that's not worth anyone's time for an op we've never
seen used.

Acked-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22083>