tgsi: add properties for fragment coord conventions (v3)

Changes in v3:
- Documented the new properties
- Added comments for property values
- Rebased to current master

Changes in v2:
- Caps are added in a separate, subsequent patch

This adds two TGSI fragment program properties that indicate the
fragment coord conventions.

The properties behave as described in the extension spec for
GL_ARB_fragment_coord_conventions, but the default origin in
upper left instead of lower left as in OpenGL.

The syntax is:
PROPERTY FS_COORD_ORIGIN [UPPER_LEFT|LOWER_LEFT]
PROPERTY FS_COORD_PIXEL_CENTER [HALF_INTEGER|INTEGER]

The names have been chosen for consistency with the GS properties
and the OpenGL extension spec.

The defaults are of course the previously assumed conventions:
UPPER_LEFT and HALF_INTEGER.

src/gallium/include/pipe/p_shader_tokens.h

@@ -170,7 +170,9 @@ union tgsi_immediate_data
 #define TGSI_PROPERTY_GS_INPUT_PRIM          0
 #define TGSI_PROPERTY_GS_OUTPUT_PRIM         1
 #define TGSI_PROPERTY_GS_MAX_VERTICES        2
-#define TGSI_PROPERTY_COUNT                  3
+#define TGSI_PROPERTY_FS_COORD_ORIGIN        3
+#define TGSI_PROPERTY_FS_COORD_PIXEL_CENTER  4
+#define TGSI_PROPERTY_COUNT                  5
 
 struct tgsi_property {
    unsigned Type         : 4;  /**< TGSI_TOKEN_TYPE_PROPERTY */
@@ -179,6 +181,12 @@ struct tgsi_property {
    unsigned Padding      : 12;
 };
 
+#define TGSI_FS_COORD_ORIGIN_UPPER_LEFT 0
+#define TGSI_FS_COORD_ORIGIN_LOWER_LEFT 1
+
+#define TGSI_FS_COORD_PIXEL_CENTER_HALF_INTEGER 0
+#define TGSI_FS_COORD_PIXEL_CENTER_INTEGER 1
+
 struct tgsi_property_data {
    unsigned Data;
 };