Use virtual dev-mode switch when told to.

If VbInit() is instructed to look at a virtual dev-mode switch, then it will
use value contained in the TPM's firmware space instead of a hardware GPIO
to determine if developer mode is enabled.

This change just makes it look. It doesn't provide a way to actually set
the value in the TPM. VbInit() isn't being told to look yet, either. Those
changes are coming.

BUG=chrome-os-partner:9706
TEST=none

The usual sanity-check applies:

  make
  make runtests

But to actually test that this stuff is working IRL requires special tweaks
to other components and monitoring the serial debug output from both EC and
CPU. We'll save the hands-on tests for when it's all done.

Change-Id: Ie485ad2180224e192238bf2a5dbf95bbcb9130f9
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/23067
Reviewed-by: Randall Spangler <rspangler@chromium.org>

firmware/include/vboot_api.h

@@ -165,6 +165,10 @@ typedef struct VbCommonParams {
 /* Calling firmware supports read only firmware for normal/developer
  * boot path. */
 #define VB_INIT_FLAG_RO_NORMAL_SUPPORT   0x00000020
+/* This platform does not have a physical dev-switch, so we must rely on a
+ * virtual switch (kept in the TPM) instead. When this flag is set,
+ * VB_INIT_FLAG_DEV_SWITCH_ON is ignored. */
+#define VB_INIT_FLAG_VIRTUAL_DEV_SWITCH  0x00000040
 
 /* Output flags for VbInitParams.out_flags.  Used to indicate
  * potential boot paths and configuration to the calling firmware