Change in coreboot[master]: soc/intel/elkhartlake: Make use of is_devfn_enabled()

[Angel Pons (Code Review)]

Attention is currently required from: Furquan Shaikh, Tim Wawrzynczak, Subrata Banik, Patrick Rudolph.
Angel Pons has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/55331 )

Change subject: soc/intel/elkhartlake: Make use of is_devfn_enabled()
......................................................................

Patch Set 5:

(1 comment)

File src/soc/intel/elkhartlake/fsp_params.c:

https://review.coreboot.org/c/coreboot/+/55331/comment/25111452_184c0efc 
PS5, Line 195: /* Enable xDCI controller if enabled in devicetree and allowed */
             : 	dev = pcidev_path_on_root(PCH_DEVFN_USBOTG);
             : 	if (dev) {
             : 		if (!xdci_can_enable())
             : 			dev->enabled = 0;
             : 
             : 		params->XdciEnable = dev->enabled;
             : 	} else {
             : 		params->XdciEnable = 0;
             : 	}
             :
> I wasn't sure if the enumeration was important or not, seems it is, Ack

It's best to handle this particular case separately because the implications of changing its behavior aren't obvious. If testing shows that clearing `dev->enabled` doesn't matter, it could be removed. But this is best discussed in a different commit: this one is just refactoring code without altering its behavior.