gpiolib-acpi: make sure we trigger edge events at least once on boot

On some systems using edge triggered ACPI Event Interrupts, the initial
state at boot is not setup by the firmware, instead relying on the edge
irq event handler running at least once to setup the initial state.

2 known examples of this are:

1) The Surface 3 has its _LID state controlled by an ACPI operation region
 triggered by a GPIO event:

 OperationRegion (GPOR, GeneralPurposeIo, Zero, One)
 Field (GPOR, ByteAcc, NoLock, Preserve)
 {
     Connection (
         GpioIo (Shared, PullNone, 0x0000, 0x0000, IoRestrictionNone,
             "\\_SB.GPO0", 0x00, ResourceConsumer, ,
             )
             {   // Pin list
                 0x004C
             }
     ),
     HELD,   1
 }

 Method (_E4C, 0, Serialized)  // _Exx: Edge-Triggered GPE
 {
     If ((HELD == One))
     {
         ^^LID.LIDB = One
     }
     Else
     {
         ^^LID.LIDB = Zero
         Notify (LID, 0x80) // Status Change
     }

     Notify (^^PCI0.SPI1.NTRG, One) // Device Check
 }

 Currently, the state of LIDB is wrong until the user actually closes or
 open the cover. We need to trigger the GPIO event once to update the
 internal ACPI state.

 Coincidentally, this also enables the Surface 2 integrated HID sensor hub
 which also requires an ACPI gpio operation region to start initialization.

2) Various Bay Trail based tablets come with an external USB mux and
 TI T1210B USB phy to enable USB gadget mode. The mux is controlled by a
 GPIO which is controlled by an edge triggered ACPI Event Interrupt which
 monitors the micro-USB ID pin.

 When the tablet is connected to a PC (or no cable is plugged in), the ID
 pin is high and the tablet should be in gadget mode. But the GPIO
 controlling the mux is initialized by the firmware so that the USB data
 lines are muxed to the host controller.

 This means that if the user wants to use gadget mode, the user needs to
 first plug in a host-cable to force the ID pin low and then unplug it
 and connect the tablet to a PC, to get the ACPI event handler to run and
 switch the mux to device mode,

This commit fixes both by running the event-handler once on boot.

Note that the running of the event-handler is done from a late_initcall,
this is done because the handler AML code may rely on OperationRegions
registered by other builtin drivers. This avoids errors like these:

[    0.133026] ACPI Error: No handler for Region [XSCG] ((____ptrval____)) [GenericSerialBus] (20180531/evregion-132)
[    0.133036] ACPI Error: Region GenericSerialBus (ID=9) has no handler (20180531/exfldio-265)
[    0.133046] ACPI Error: Method parse/execution failed \_SB.GPO2._E12, AE_NOT_EXIST (20180531/psparse-516)

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
[hdegoede: Document BYT USB mux reliance on initial trigger]
[hdegoede: Run event handler from a late_initcall, rather then immediately]
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>