drm/amd/display: Add comments to v_total calculation and drop legacy TODO

[WHY & HOW]
This commit just adds some simple comments to help understand the
calculation of V total duration for Freesync. Also, remove a legacy TODO
comment from link service type.

Acked-by: Alex Hung <[e-mail]>
Signed-off-by: Rodrigo Siqueira <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 	enum dc_pre_emphasis *pre_emphasis;
 	enum dc_post_cursor2 *post_cursor2;
 	bool should_set_fec_ready;
-	/* TODO - factor lane_settings out because it changes during LT */
 	union dc_dp_ffe_preset *ffe_preset;
 
 	uint16_t cr_pattern_time;

drivers/gpu/drm/amd/display/modules/freesync/freesync.c

···
 	if (duration_in_us > vrr->max_duration_in_us)
 		duration_in_us = vrr->max_duration_in_us;
 
-	if (dc_is_hdmi_signal(stream->signal)) {
+	if (dc_is_hdmi_signal(stream->signal)) { // change for HDMI to comply with spec
 		uint32_t h_total_up_scaled;
 
 		h_total_up_scaled = stream->timing.h_total * 10000;
 		v_total = div_u64((unsigned long long)duration_in_us
 					* stream->timing.pix_clk_100hz + (h_total_up_scaled - 1),
-					h_total_up_scaled);
+					h_total_up_scaled); //ceiling for MMax and MMin for MVRR
 	} else {
 		v_total = div64_u64(div64_u64(((unsigned long long)(
 					duration_in_us) * (stream->timing.pix_clk_100hz / 10)),