nvc0: add support for handling indirect draws with attrib conversion

The hardware does not natively support FIXED and DOUBLE formats. If
those are used in an indirect draw, they have to be converted. Our
conversion tries to be clever about only converting the data that's
needed. However for indirect, that won't work.

Given that DOUBLE or FIXED are highly unlikely to ever be used with
indirect draws, read the indirect buffer on the CPU and issue draws
directly.

Fixes the failing dEQP-GLES31.functional.draw_indirect.random.* tests.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: 19.0 <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 399215eb)