fsp_baytrail: Change A, A, A, A IRQ routing to A, A, A, B

Devices that have their interrupt routing set to A, A, A, A don't get
any interrupt values assigned because that series evaluates to 0.  The
code that sets the interrupt values checks to make sure a value is set
by verifying that it's not 0.  On Bay Trail, these are all
single-function graphics devices, so by changing one of the unused
interrupt lines from A to any other value, it assigns the values
correctly.

This issue did not affect ACPI interrupt routing.

This is just a workaround, and the root issue still needs to be fixed.

Change-Id: I78866e3e0079435037e457a4fb04979254b56ee2
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12629
Tested-by: build bot (Jenkins)
Reviewed-by: Ben Gardner <gardner.ben@gmail.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/src/mainboard/siemens/mc_tcu3/irqroute.h b/src/mainboard/siemens/mc_tcu3/irqroute.h
index e3523e9..8b6a46e 100644
--- a/src/mainboard/siemens/mc_tcu3/irqroute.h
+++ b/src/mainboard/siemens/mc_tcu3/irqroute.h
@@ -44,8 +44,9 @@
 #define PCIE_BRIDGE_IRQ_ROUTES \
 	PCIE_BRIDGE_DEV(RP, BRIDGE1_DEV,    E, F, G, H)
 
+/* Devices set as A, A, A, A evaluate as 0, and don't get set */
 #define PCI_DEV_PIRQ_ROUTES \
-	PCI_DEV_PIRQ_ROUTE(GFX_DEV,     A, A, A, A), \
+	PCI_DEV_PIRQ_ROUTE(GFX_DEV,     A, A, A, B), \
 	PCI_DEV_PIRQ_ROUTE(EMMC_DEV,    D, E, F, G), \
 	PCI_DEV_PIRQ_ROUTE(SDIO_DEV,    B, A, A, A), \
 	PCI_DEV_PIRQ_ROUTE(SD_DEV,      C, A, A, A), \