Check for enable_lspci option and don't use if it's set to False.  Also check to ensure /proc/bus/pci exists before using lspci, doesn't exist on certain machines eg. Raspberry Pi, so lspci will fail even if installed.
Merge pull request #16185 from garethgreenaway/15961_lspci_on_raspberry_pi

Changes to salt/grains/core.py