freedreno/ir3: assert that only single address

freedreno/ir3: assert that only single address

An instruction can reference only a single address register value.
Add an assert to catch bugs.

Also, address value should also be local to the same block as the
instruction.

(The one spot where changing the instruction address is actually legit
needs to clear the address first.)

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Eric Anholt <eric@anholt.net>