ACPI: GED: add support for _Exx / _Lxx handler methods

commit ea6f3af4c5e63f6981c0b0ab8ebec438e2d5ef40 upstream.

Per the ACPI spec, interrupts in the range [0, 255] may be handled
in AML using individual methods whose naming is based on the format
_Exx or _Lxx, where xx is the hex representation of the interrupt
index.

Add support for this missing feature to our ACPI GED driver.

Cc: v4.9+ <stable@vger.kernel.org> # v4.9+
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>