drm/amd/display: Add DFS reference clock field

Add to clk_mgr_internal struct, for future use.
Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/inc/hw/clk_mgr_internal.h

@@ -216,6 +216,8 @@ struct clk_mgr_internal {
 	bool dfs_bypass_enabled;
 	/* True if the DFS-bypass feature is enabled and active. */
 	bool dfs_bypass_active;
+
+	uint32_t dfs_ref_freq_khz;
 	/*
 	 * Cache the display clock returned by VBIOS if DFS-bypass is enabled.
 	 * This is basically "Crystal Frequency In KHz" (XTALIN) frequency