soc/intel: Replace uses of dev_find_slot()

To call dev_find_slot(0, xx) in romstage can produce
invalid results since PCI bus enumeration has not
been progressed yet.

Replace this with method that relies on bus topology
that walks the root bus only.

Change-Id: I2883610059bb9fa860bba01179e7d5c58cae00e5
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33996
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/soc/intel/skylake/irq.c

@@ -223,7 +223,7 @@ void soc_irq_settings(FSP_SIL_UPD *params)
 
 	uint32_t i, intdeventry;
 	u8 irq_config[PCH_MAX_IRQ_CONFIG];
-	const struct device *dev = dev_find_slot(0, PCH_DEVFN_LPC);
+	const struct device *dev = pcidev_path_on_root(PCH_DEVFN_LPC);
 	const struct soc_intel_skylake_config *config = dev->chip_info;
 
 	/* Get Device Int Count */