Arrays of constants can be dynamically indexed, so they can't be
propagated by value and handled as literals like other constants.
Instead we store them in the constant register file.

Change-Id: Idcee033d694b20d047c70e2d13974e5a6dce127b
Reviewed-on: https://swiftshader-review.googlesource.com/15488Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>