eth: fbnic: Add register init to set PCIe/Ethernet device config

As a part of enabling the device the first step is to configure the AXI and
Ethernet interfaces to allow for basic traffic. This consists of
configuring several registers related to the PCIe and Ethernet FIFOs as
well as configuring the handlers for moving traffic between entities.

Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Link: https://patch.msgid.link/172079936376.1778861.15942501417449077552.stgit@ahduyck-xeon-server.home.arpa


Signed-off-by: Jakub Kicinski <kuba@kernel.org>