vc/google: Add and use POST_CODE_CLEAR definition

The CR50 code clears the post code value.  Add this as a #define.

Signed-off-by: Martin Roth <gaumless@gmail.com>
Change-Id: If3b73a3159ac8ac9ab08c6ff705b0ca289ab453c
Reviewed-on: https://review.coreboot.org/c/coreboot/+/71592
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jon Murphy <jpmurphy@google.com>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>

src/commonlib/include/commonlib/console/post_codes.h

@@ -27,6 +27,12 @@
 #ifndef POST_CODES_H
 #define POST_CODES_H
 
+/**
+ * \brief Not an actual post-code - used to clear port80h
+ *
+ */
+#define POST_CODE_CLEAR				0x00
+
 /**
  * \brief  Entry into 'crt0.s'. reset code jumps to here
  *