gallium: add double opcodes and TGSI execution (v4.2)

gallium: add double opcodes and TGSI execution (v4.2)

This patch adds support for a set of double opcodes
to TGSI. It is an update of work done originally
by Michal Krol on the gallium-double-opcodes branch.

The opcodes have a hint where they came from in the
header file.

v2: add unsigned/int <-> double
v2.1:  update docs.

v3: add DRSQ (Glenn), fix review comments (Glenn).

v4: drop DDIV
v4.1: cleanups, fix some docs bugs, (Ilia)
      rework store_dest and fetch_source fns. (Ilia)
4.2: fixup float comparisons (Ilia)

This is based on code by Michael Krol <michal@vmware.com>

Roland and Glenn also reviewed earlier versions.

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Dave Airlie <airlied@redhat.com>