AMD Thatcher: fix issue 'S3 fails to suspend after wake up from USB keyboard'

This issue can be reproduced in Linux by the following steps:
1) use pm-suspend to suspend.
2) use USB keyboard to wake up.
3) use pm-suspend to suspend. FAIL To SUSPEND.

The cause of this issue is:
USB devices use bit 11(0x0b) of GP0_STS represents S3 wake up event,
but this bit is not clear after wake up. So OS thinks there is a
wake up signal and wake up immediately.

In this patch, I add AcpiGpe0Blk using MMIO access and write 1
on bit 11. Write 1 to clear as spec says.
I have tested on Thatcher

The same change was done for AMD Parmer in commit »AMD Parmer:
fix issue 'S3 fails to suspend after wake up from USB keyboard'
(03901124) [1].

[1] http://review.coreboot.org/#/c/3347/
    (Change-Id: Iec3078bf29de99683e7cd3ef4e178fbeb4dc09c1)

Change-Id: Iaef39237497ef896d0f186e8f5522222c0ce6cb7
Signed-off-by: Siyuan Wang <SiYuan.Wang@amd.com>
Signed-off-by: Siyuan Wang <wangsiyuanbuaa@gmail.com>
Reviewed-on: http://review.coreboot.org/3374
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/amd/thatcher/dsdt.asl

@@ -202,6 +202,14 @@ DefinitionBlock (
 	/* PM1 Event Block
 	* First word is PM1_Status, Second word is PM1_Enable
 	*/
+
+	/* AcpiGpe0Blk */
+	OperationRegion(GP0B, SystemMemory, 0xfed80814, 0x04)
+		Field(GP0B, ByteAcc, NoLock, Preserve) {
+		, 11,
+		USBS, 1,
+	}
+
 	Scope(\_SB) {
 		/* PCIe Configuration Space for CONFIG_MMCONF_BUS_NUMBER busses */
 		OperationRegion(PCFG, SystemMemory, PCBA, PCLN)
@@ -844,6 +852,8 @@ DefinitionBlock (
 		*	Store(Arg0, Index(WKST,1))
 		* }
 		*/
+		/* clear USB wake up signal */
+		Store(1, USBS)
 		Return(WKST)
 	} /* End Method(\_WAK) */