drm/dsc: Define Rate Control values that do not change over configurations

DSC has some Rate Control values that remain constant
across all configurations. These are as per the DSC
standard.

v3:
* Define them in drm_dsc.h as they are
DSC constants (Manasi)
v2:
* Add DP_DSC_ prefix (Jani Nikula)

Cc: [e-mail]
Cc: Manasi Navare <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Cc: Ville Syrjala <[e-mail]>
Cc: Gaurav K Singh <[e-mail]>
Cc: Harry Wentland <[e-mail]>
Signed-off-by: Srivatsa, Anusha <[e-mail]>
Signed-off-by: Manasi Navare <[e-mail]>
Reviewed-by: Manasi Navare <[e-mail]>
Acked-by: Sean Paul <[e-mail]> (For merging through
drm-intel)
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

include/drm/drm_dsc.h

···
 #define DSC_SCALE_DECREMENT_INTERVAL_MAX	4095
 #define DSC_RANGE_BPG_OFFSET_MASK		0x3f
 
+/* DSC Rate Control Constants */
+#define DSC_RC_MODEL_SIZE_CONST		    8192
+#define DSC_RC_EDGE_FACTOR_CONST	    6
+#define DSC_RC_TGT_OFFSET_HI_CONST	    3
+#define DSC_RC_TGT_OFFSET_LO_CONST	    3
+
 /* Configuration for a single Rate Control model range */
 struct drm_dsc_rc_range_parameters {
 	/* Min Quantization Parameters allowed for this range */