feat: HDMI refresh boost per display, with a Saved displays screen

Rates are saved per display (EDID ID) and loaded by the hotplug script
for whichever display is connected. The item is on only while the
connected display is boosted; unticking removes just that one. The app
lists the saved displays and removes any of them (hdmi-forget).

lib/steam-machine.sh

@@ -163,7 +163,12 @@ kpin_enable() {
     fi
 }
 
-kpin_disable() { remove_kernel_pin; }
+kpin_disable() {
+    # Saved HDMI refresh boost EDIDs are for the pinned kernel only (newer
+    # ones read the whole EDID), also those of displays not connected now.
+    [[ -n "$(hdmi_saved)" ]] && hdmi_forget all
+    remove_kernel_pin
+}
 
 install_kernel_headers() {
     # DKMS can only build leds-valve against kernels whose headers are