SPI: opmenu special case for WREN as atomic prefix

The code that attempts to use the opmenu needs to have a special
case for write enable now that it is handled as an atomic prefix
and not as a standalone opcode.

To test, ensure that runtime SPI write via ELOG is successful by
checking the event log for a kernel shutdown reason code:

5 | 2012-08-27 11:09:48 | Kernel Event | Clean Shutdown
6 | 2012-08-27 11:09:50 | System boot | 26
7 | 2012-08-27 11:09:50 | System Reset

Change-Id: I527638ef3e2a5ab100192c5be6e6b3b40916295a
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/1710
Reviewed-by: Marc Jones <marcj303@gmail.com>
Tested-by: build bot (Jenkins)
diff --git a/src/southbridge/intel/bd82x6x/spi.c b/src/southbridge/intel/bd82x6x/spi.c
index 5903fd8..2e88932 100644
--- a/src/southbridge/intel/bd82x6x/spi.c
+++ b/src/southbridge/intel/bd82x6x/spi.c
@@ -505,6 +505,10 @@
 		uint8_t optype;
 		uint16_t opcode_index;
 
+		/* Write Enable is handled as atomic prefix */
+		if (trans->opcode == SPI_OPCODE_WREN)
+			return 0;
+
 		read_reg(cntlr.opmenu, opmenu, sizeof(opmenu));
 		for (opcode_index = 0; opcode_index < cntlr.menubytes;
 				opcode_index++) {
@@ -623,7 +627,7 @@
 	if ((with_address = spi_setup_offset(&trans)) < 0)
 		return -1;
 
-	if (!ichspi_lock && trans.opcode == 0x06) {
+	if (!ichspi_lock && trans.opcode == SPI_OPCODE_WREN) {
 		/*
 		 * Treat Write Enable as Atomic Pre-Op if possible
 		 * in order to prevent the Management Engine from