i965: Convert scalar_* flags to a scalar_stage array.

i965: Convert scalar_* flags to a scalar_stage array.

I was going to add scalar_tcs and scalar_tes flags, and then thought
better of it and decided to convert this to an array.  Simpler.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>