drm/i915: Unionize dpll_hw_state

intel_dpll_hw_state contains space for all possible PLL
register values across all platforms. That is rather wasteful
as each machine only needs to store the registers values
that are appropriate for the platform.

Turn intel_dpll_hw_state into a union so that we don't
waste memory for the register values of other platforms.

And let's use an anonymous union so that we don't have
to do tons of s/struct/union/ all over the place.

pahole:
 struct intel_dpll_hw_state {
-       struct i9xx_dpll_hw_state  i9xx;                 /*     0    16 */
-       struct hsw_dpll_hw_state   hsw;                  /*    16     8 */
-       struct skl_dpll_hw_state   skl;                  /*    24    12 */
-       struct bxt_dpll_hw_state   bxt;                  /*    36    44 */
-       /* --- cacheline 1 boundary (64 bytes) was 16 bytes ago --- */
-       struct icl_dpll_hw_state   icl;                  /*    80    60 */
+       union {
+               struct i9xx_dpll_hw_state i9xx;          /*     0    16 */
+               struct hsw_dpll_hw_state hsw;            /*     0     8 */
+               struct skl_dpll_hw_state skl;            /*     0    12 */
+               struct bxt_dpll_hw_state bxt;            /*     0    44 */
+               struct icl_dpll_hw_state icl;            /*     0    60 */
+       };                                               /*     0    60 */

-       /* size: 140, cachelines: 3, members: 5 */
-       /* last cacheline: 12 bytes */
+       /* size: 60, cachelines: 1, members: 1 */
+       /* last cacheline: 60 bytes */
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240412182703.19916-18-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_dpll_mgr.h

@@ -230,11 +230,13 @@ struct icl_dpll_hw_state {
 };
 
 struct intel_dpll_hw_state {
-	struct i9xx_dpll_hw_state i9xx;
-	struct hsw_dpll_hw_state hsw;
-	struct skl_dpll_hw_state skl;
-	struct bxt_dpll_hw_state bxt;
-	struct icl_dpll_hw_state icl;
+	union {
+		struct i9xx_dpll_hw_state i9xx;
+		struct hsw_dpll_hw_state hsw;
+		struct skl_dpll_hw_state skl;
+		struct bxt_dpll_hw_state bxt;
+		struct icl_dpll_hw_state icl;
+	};
 };
 
 /**