drm/i915: disable PSR by default on HSW/BDW

We've been ignoring the poor bugzilla reporters that say PSR causes
system lockups and all other sorts of problems. The earliest bug
report is from April, so I think we can use the "revert the offending
commit if no fixes are presented within 8 months" rule here.

Fixes: 9b58e352b463 ("drm/i915: Enable PSR by default on Haswell and Broadwell.")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97602
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97515
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96736
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96704
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96569
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95176
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94985
Cc: <[e-mail]> # v4.6+
Cc: Rodrigo Vivi <[e-mail]>
Cc: Jim Bride <[e-mail]>
Signed-off-by: Paulo Zanoni <[e-mail]>
Acked-by: Rodrigo Vivi <[e-mail]>
Reviewed-by: Rodrigo Vivi <[e-mail]>
Acked-by: Jani Nikula <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]
(cherry picked from commit 2ee7dc497e348eecbb82adbb1ea9e9a7e29fe921)
Signed-off-by: Jani Nikula <[e-mail]>

drivers/gpu/drm/i915/intel_psr.c

···
 	dev_priv->psr_mmio_base = IS_HASWELL(dev_priv) ?
 		HSW_EDP_PSR_BASE : BDW_EDP_PSR_BASE;
 
-	/* Per platform default */
-	if (i915.enable_psr == -1) {
-		if (IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv))
-			i915.enable_psr = 1;
-		else
-			i915.enable_psr = 0;
-	}
+	/* Per platform default: all disabled. */
+	if (i915.enable_psr == -1)
+		i915.enable_psr = 0;
 
 	/* Set link_standby x link_off defaults */
 	if (IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv))