Add PCIe port ID verification in Marvell PCIe

[bsz_semihalf.com]

Summary

This commit introduces recognition of 'port-id' field, present in
Linux-compliant DTS files.

Submitted by: Marcin Mazurek <[e-mail]>
Obtained from: Semihalf
Sponsored by: Stormshield
Differential revision:
Reviewed by:

[andrew]

sys/arm/mv/mv_pci.c

434

Is it ever the case this will return < 0 when the property exists? You could use this to check if it exists, but is empty.