pcie-bifurcation: Pass configuration file path

Summary:
On systems with detachable HPMs, there are different system setups
where not all HPMs may be present. We shouldn't be checking the
bifurcation on missing HPMs as this will generate unused mappings, and
this process may potentially fail to store the generated files for a
missing HPM if the related directory doesn't exist.

Provide an option to pass the configuration file path.

Google-Bug-Id: 409831464
Change-Id: Ibac867f0ed82c9db4da119d5bf9c5e39f94ba367
Signed-off-by: Kyle Nieman <kyle.nieman@fii-na.corp-partner.google.com>