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/icelake/memmap.c

@@ -218,7 +218,7 @@ static uintptr_t calculate_dram_base(size_t *reserved_mem_size)
 	uintptr_t dram_base;
 	const struct device *dev;
 
-	dev = dev_find_slot(0, PCI_DEVFN(SA_DEV_SLOT_IGD, 0));
+	dev = pcidev_on_root(SA_DEV_SLOT_IGD, 0);
 	if (!dev)
 		die_with_post_code(POST_HW_INIT_FAILURE,
 				   "ERROR - IGD device not found!");