soc/intel/skylake: Lock sideband access in coreboot and not in FSP

The Sideband Acces locking code is skipped from FSP by setting an
FSP-S UPD called PchSbAccessUnlock. This locking is being done in
coreboot during finalize.c.

This is done because coreboot was failing to disable HECI1 device
using Sideband interface during finalize.c if FSP already locks
the Sideband access mechanism before that.

So, as a solution, coreboot passes an UPD to skip the locking
in FSP, and in finalize.c, after disabling HECI, it removes the
Sideband access.

BUG=b:63877089
BRANCH=none
TEST=Build and boot poppy to check lspci not showing Intel ME
controller in the PCI device list.

Change-Id: I8dba4c97480200507969b0f2873337f97bd2ff6a
Signed-off-by: Barnali Sarkar <barnali.sarkar@intel.com>
Reviewed-on: https://review.coreboot.org/20956
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/soc/intel/skylake/chip_fsp20.c

@@ -203,6 +203,14 @@ void platform_fsp_silicon_init_params_cb(FSPS_UPD *supd)
 	tconfig->PchLockDownGlobalSmi = config->LockDownConfigGlobalSmi;
 	tconfig->PchLockDownBiosInterface = config->LockDownConfigBiosInterface;
 	tconfig->PchLockDownRtcLock = config->LockDownConfigRtcLock;
+	/*
+	 * To disable HECI, the Psf needs to be left unlocked
+	 * by FSP till end of post sequence. Based on the devicetree
+	 * setting, we set the appropriate PsfUnlock policy in FSP,
+	 * do the changes and then lock it back in coreboot during finalize.
+	 */
+	tconfig->PchSbAccessUnlock = (config->HeciEnabled == 0) ? 1 : 0;
+
 	params->PchLockDownBiosLock = config->LockDownConfigBiosLock;
 	params->PchLockDownSpiEiss = config->LockDownConfigSpiEiss;
 	params->PchSubSystemVendorId = config->PchConfigSubSystemVendorId;