aco: implement 64-bit VGPR constant copies in handle_operands()

aco: implement 64-bit VGPR constant copies in handle_operands()

64-bit VGPR constant copies can happen because of 64-bit constant copy
propagation. Since this optimization is beneficial and more annoying to
deal with in the optimizer, I've implemented 64-bit VGPR constant copies
in handle_operands().

This also sets copy_operation::size correctly for 64-bit constant copies.

Cc: 20.0 <mesa-stable@lists.freedesktop.org>
Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4260>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4260>