intel/elk: Use REG_CLASS_COUNT

Fixes: d44462c08d ("intel/elk: Fork Gfx8- compiler by copying existing code")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30314>
(cherry picked from commit a3714b55f4)

.pick_status.json

@@ -1444,7 +1444,7 @@
         "description": "intel/elk: Use REG_CLASS_COUNT",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "d44462c08d8858a4ab2dc37b311cc69501adb0dc",
         "notes": null

src/intel/compiler/elk/elk_compiler.h

@@ -47,6 +47,8 @@ struct shader_info;
 struct nir_shader_compiler_options;
 typedef struct nir_shader nir_shader;
 
+#define REG_CLASS_COUNT 20
+
 struct elk_compiler {
    const struct intel_device_info *devinfo;
 
@@ -74,7 +76,7 @@ struct elk_compiler {
        * Array of the ra classes for the unaligned contiguous register
        * block sizes used, indexed by register size.
        */
-      struct ra_class *classes[16];
+      struct ra_class *classes[REG_CLASS_COUNT];
 
       /**
        * ra class for the aligned barycentrics we use for PLN, which doesn't

src/intel/compiler/elk/elk_fs_reg_allocate.cpp

@@ -34,8 +34,6 @@
 
 using namespace elk;
 
-#define REG_CLASS_COUNT 20
-
 static void
 assign_reg(const struct intel_device_info *devinfo,
            unsigned *reg_hw_locations, elk_fs_reg *reg)