ACPI / ACPICA: Do not execute _PRW methods during initialization

Currently, during initialization ACPICA walks the entire ACPI
namespace in search of any device objects with assciated _PRW
methods.  All of the _PRW methods found are executed in the process
to extract the GPE information returned by them, so that the GPEs in
question can be marked as "able to wakeup" (more precisely, the
ACPI_GPE_CAN_WAKE flag is set for them).  The only purpose of this
exercise is to avoid enabling the CAN_WAKE GPEs automatically, even
if there are _Lxx/_Exx methods associated with them.  However, it is
both costly and unnecessary, because the host OS has to execute the
_PRW methods anyway to check which devices can wake up the system
from sleep states.  Moreover, it then uses full information
returned by _PRW, including the GPE information, so it can take care
of disabling the GPEs if necessary.

Remove the code that walks the namespace and executes _PRW from
ACPICA and modify comments to reflect that change.  Make
acpi_bus_set_run_wake_flags() disable GPEs for wakeup devices
so that they don't cause spurious wakeup events to be signaled.
This not only reduces the complexity of the ACPICA initialization
code, but in some cases it should reduce the kernel boot time as
well.

Unfortunately, for this purpose we need a new ACPICA function,
acpi_gpe_can_wake(), to be called by the host OS in order to disable
the GPEs that can wake up the system and were previously enabled by
acpi_ev_initialize_gpe_block() or acpi_ev_update_gpes() (such a GPE
should be disabled only once, because the initialization code enables
it only once, but it may be pointed to by _PRW for multiple devices
and that's why the additional function is necessary).

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>

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