i965/fs: Define new shader opcode to set rounding modes

Although it is possible to emit them directly as AND/OR on brw_fs_nir,
having a specific opcode makes it easier to remove duplicate settings
later.

v2: (Curro)
  - Set thread control to 'switch' when using the control register
  - Use a single SHADER_OPCODE_RND_MODE opcode taking an immediate
    with the rounding mode.
  - Avoid magic numbers setting rounding mode field at control register.
v3: (Curro)
  - Remove redundant and add missing whitespace lines.
  - Match printing instruction to IR opcode "rnd_mode"

v4: (Topi Pohjolainen)
  - Fix code style.

Signed-off-by:  Alejandro Piñeiro <apinheiro@igalia.com>
Signed-off-by:  Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/compiler/brw_eu.h

@@ -510,6 +510,10 @@ brw_broadcast(struct brw_codegen *p,
               struct brw_reg src,
               struct brw_reg idx);
 
+void
+brw_rounding_mode(struct brw_codegen *p,
+                  enum brw_rnd_mode mode);
+
 /***********************************************************************
  * brw_eu_util.c:
  */