mb/emulation/qemu-q35: Define and use MMCONF_BUS_NUMBER

Also refactor the machine type checks to avoid code duplication.

Tested, still boots to payload with 256, 128 and 64 busses.

Change-Id: Ib394ba605bbfeee75aa645e989c23034cceff348
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50025
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/emulation/qemu-q35/romstage.c b/src/mainboard/emulation/qemu-q35/romstage.c
index e9637e8..c9bc339 100644
--- a/src/mainboard/emulation/qemu-q35/romstage.c
+++ b/src/mainboard/emulation/qemu-q35/romstage.c
@@ -8,20 +8,12 @@
 
 #include "q35.h"
 
-static void mainboard_machine_check(void)
-{
-	/* Check that MCFG is active. If it's not qemu was started for machine PC */
-	if (!CONFIG(BOOTBLOCK_CONSOLE) &&
-	    (pci_read_config32(HOST_BRIDGE, D0F0_PCIEXBAR_LO) !=
-	     (CONFIG_MMCONF_BASE_ADDRESS | 1)))
-		die("You must run qemu for machine Q35 (-M q35)");
-}
-
 void mainboard_romstage_entry(void)
 {
 	i82801ix_early_init();
 
-	mainboard_machine_check();
+	if (!CONFIG(BOOTBLOCK_CONSOLE))
+		mainboard_machine_check();
 
 	cbmem_recovery(0);
 }