drm/amd/display: WBSCL filter init calculation fixes

* Previous code did some calculations with a mix of normal integers and
  integers aligned as U2.24 fixed-point values.
* There were bugs in the conversion of the final result into the
  S4.19 values required for the registers.

Signed-off-by: Ken Chalmers <ken.chalmers@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c

@@ -593,3 +593,12 @@ uint32_t dal_fixed31_32_clamp_u0d10(
 {
 	return clamp_ux_dy(arg.value, 0, 10, 1);
 }
+
+int32_t dal_fixed31_32_s4d19(
+	struct fixed31_32 arg)
+{
+	if (arg.value < 0)
+		return -(int32_t)ux_dy(dal_fixed31_32_abs(arg).value, 4, 19);
+	else
+		return ux_dy(arg.value, 4, 19);
+}

drivers/gpu/drm/amd/display/include/fixed31_32.h

@@ -470,4 +470,7 @@ uint32_t dal_fixed31_32_clamp_u0d14(
 uint32_t dal_fixed31_32_clamp_u0d10(
 	struct fixed31_32 arg);
 
+int32_t dal_fixed31_32_s4d19(
+	struct fixed31_32 arg);
+
 #endif