drm/i915: Document that PLANE_CHICKEN are for tgl+

Add tgl+ comments to the PLANE_CHICKEN registers which
I apparently forgot to add when defining the registers.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230329190445.13456-2-ville.syrjala@linux.intel.comReviewed-by: Imre Deak <imre.deak@intel.com>

drivers/gpu/drm/i915/i915_reg.h

@@ -4026,8 +4026,8 @@
 #define   PLANE_COLOR_ALPHA_DISABLE			REG_FIELD_PREP(PLANE_COLOR_ALPHA_MASK, 0)
 #define   PLANE_COLOR_ALPHA_SW_PREMULTIPLY		REG_FIELD_PREP(PLANE_COLOR_ALPHA_MASK, 2)
 #define   PLANE_COLOR_ALPHA_HW_PREMULTIPLY		REG_FIELD_PREP(PLANE_COLOR_ALPHA_MASK, 3)
-#define _PLANE_CHICKEN_1_A			0x7026C
-#define _PLANE_CHICKEN_2_A			0x7036C
+#define _PLANE_CHICKEN_1_A			0x7026C /* tgl+ */
+#define _PLANE_CHICKEN_2_A			0x7036C /* tgl+ */
 #define   PLANE_CHICKEN_DISABLE_DPT		REG_BIT(19) /* mtl+ */
 #define _PLANE_BUF_CFG_1_A			0x7027c
 #define _PLANE_BUF_CFG_2_A			0x7037c