PCI/switchtec: Separate Gen3 register structures into unions

Since the sys_info and flash_info registers differ significantly in Gen4
hardware, separate out the Gen3 registers into their own structure with a
union in the main structure.

No functional changes intended.

Link: https://lore.kernel.org/r/20200115035648.2578-5-logang@deltatee.com


Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>