Revert "drm/radeon: fix DP link training issue with second 4K monitor"

This reverts commit 1a738347.

It caused at least some Kaveri laptops to incorrectly report DisplayPort
connectors as connected.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97857
Cc: stable@vger.kernel.org
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NMichel Dänzer <michel.daenzer@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_dp_auxch.c

@@ -105,7 +105,7 @@ radeon_dp_aux_transfer_native(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg
 
 	tmp &= AUX_HPD_SEL(0x7);
 	tmp |= AUX_HPD_SEL(chan->rec.hpd);
-	tmp |= AUX_EN | AUX_LS_READ_EN | AUX_HPD_DISCON(0x1);
+	tmp |= AUX_EN | AUX_LS_READ_EN;
 
 	WREG32(AUX_CONTROL + aux_offset[instance], tmp);