brcmfmac: support NVRAMs containing pci devpaths (instead of pcie)

Recently Broadcom added support for NVRAMs with entries for multiple
PCIe devices. One of the supported formats is based on prefixes defined
like: devpath0=pcie/1/4/ and entries like 0:foo=bar 0:baz=qux etc.

Unfortunately there are also a bit older devices using different way of
defining prefixes, e.g. SmartRG SR400ac (2 x BCM43602) with entries:
devpath0=pci/1/1/
devpath1=pci/2/1
Broadcom stated this old format will never be used/supported by brcmfmac
but given the simplicity of this patch I'll insist on supporting it.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>