soc/intel: Fix regression with hidden PCI devices

Fix regression with commit
  903b40a soc/intel: Replace uses of dev_find_slot()

Platforms where FSP hides PCI devices before enumeration
may halt with error message 'PCI: dev is NULL!'.

The workaround here is to print an error message revealing
the faulty source code function and revert to old behaviour
of dev_find_slot().

Change-Id: I5eab3e7f1993b686103eaa257aacda379dc259fa
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34285
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Maxim Polyakov <max.senia.poliak@gmail.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Christian Walter <christian.walter@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/device/device_const.c

@@ -234,6 +234,18 @@ DEVTREE_CONST struct device *pcidev_on_root(uint8_t dev, uint8_t fn)
 	return pcidev_path_on_root(PCI_DEVFN(dev, fn));
 }
 
+DEVTREE_CONST struct device *pcidev_path_on_root_debug(pci_devfn_t devfn, const char *func)
+{
+	DEVTREE_CONST struct device *dev = pcidev_path_on_root(devfn);
+	if (dev)
+		return dev;
+
+	printk(BIOS_ERR, "BUG: %s requests hidden 00:%02x.%u\n", func, devfn >> 3, devfn & 7);
+
+	/* FIXME: This can return wrong device. */
+	return dev_find_slot(0, devfn);
+}
+
 /**
  * Given an SMBus bus and a device number, find the device structure.
  *