drivers/net: add SSDT ACPI declaration and WOL feature

This patch adds SSDT ACPI generator and declares _UID, _HID, _DDN and
also _PRW for WOL feature. Besides, adds a wake variable in chip
information.

BUG=b:69290148
BRANCH=None
TEST=Add register "wake" = "GPE0_PCI_EXP" in devicetree under r8168
     chip driver && dump SSDT to make sure _UID, _HID, _DDN and _PRW
     are filled correctly && put system into S3 && sudo etherwake -i
     eth0 $MAC to make sure the system could be woken up by WOL package.

Change-Id: Ibc9115e8a08ba2bfcb3ee1e34c73cf1976a6ba2d
Signed-off-by: Gaggery Tsai <gaggery.tsai@intel.com>
Reviewed-on: https://review.coreboot.org/22480
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/drivers/net/chip.h

@@ -16,6 +16,7 @@
 
 struct drivers_net_config {
 	uint16_t customized_leds;
+	unsigned wake; /* Wake pin for ACPI _PRW */
 };
 
 #endif /* __DRIVERS_R8168_CHIP_H__ */