RUNTIME_PM_DRIVER_DENYLIST: add xhci_hcd to default

Rationale: users report that USB devices are not recognized or do not
work in battery mode.

Workaround: exclude USB3 controllers from runtime pm. Additional power
consumption on unaffected laptops should be negligible.

References:
* https://linrunner.de/tlp/faq/usb.html#faq-usb-not-working-on-battery
* #436
* #587

defaults.conf

@@ -40,7 +40,7 @@ BAY_POWEROFF_ON_BAT=0
 BAY_DEVICE="sr0"
 RUNTIME_PM_ON_AC=on
 RUNTIME_PM_ON_BAT=auto
-RUNTIME_PM_DRIVER_DENYLIST="mei_me nouveau radeon"
+RUNTIME_PM_DRIVER_DENYLIST="mei_me nouveau radeon xhci_hcd"
 USB_AUTOSUSPEND=1
 USB_EXCLUDE_AUDIO=1
 USB_EXCLUDE_BTUSB=0

tlp.conf.in

@@ -390,9 +390,9 @@
 # Note: this preserves the kernel driver default, to force a certain state
 # use RUNTIME_PM_ENABLE/DISABLE instead.
 # Separate multiple drivers with spaces.
-# Default: "mei_me nouveau radeon", use "" to disable completely.
+# Default: "mei_me nouveau radeon xhci_hcd", use "" to disable completely.
 
-#RUNTIME_PM_DRIVER_DENYLIST="mei_me nouveau radeon"
+#RUNTIME_PM_DRIVER_DENYLIST="mei_me nouveau radeon xhci_hcd"
 
 # Permanently enable/disable Runtime PM for listed PCIe device addresses
 # (independent of the power source). This has priority over all preceding