eth: fbnic: add PCIe hardware statistics

eth: fbnic: add PCIe hardware statistics

Add PCIe hardware statistics support to the fbnic driver. These stats
provide insight into PCIe transaction performance and error conditions.

Which includes, read/write and completion TLP counts and DWORD counts and
debug counters for tag, completion credit and NP credit exhaustion

The stats are exposed via debugfs and can be used to monitor PCIe
performance and debug PCIe issues.

Signed-off-by: Sanman Pradhan <sanman.p211993@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20241115015344.757567-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>