i965: Replace incorrect use of GLboolean with enum brw_compression.

i965: Replace incorrect use of GLboolean with enum brw_compression.

brw_set_compression_control took a GLboolean as an argument, then
promptly used a switch statement to compare it with various enumeration
values.  Clearly it's not actually a boolean.

Introduce a new enumeration type, enum brw_compression, and use that.

Found by converting GLboolean to bool; clang then gave warnings about
switching on a boolean and ultimately duplicated case errors.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Chad Versace <chad@chad-versace.us>