FDDI: defxx: Implement dynamic CSR I/O address space selection

Recent versions of the PCI Express specification have deprecated support
for I/O transactions and actually some PCIe host bridges, such as Power
Systems Host Bridge 4 (PHB4), do not implement them.  Conversely a DEFEA
adapter can have its MMIO decoding disabled with ECU (EISA Configuration
Utility) and therefore not available for us with the resource allocation
infrastructure we implement.

However either I/O address space will always be available for use with
the DEFEA (EISA) and DEFPA (PCI) adapters and both have double address
decoding implemented in hardware for Control and Status Register access.
The two kinds of adapters can be present both at once in a single mixed
PCI/EISA system.  For the DEFTA (TURBOchannel) variant there is no issue
as there has been no port I/O address space defined for that bus.

To make people's life easier and the driver more robust remove the
DEFXX_MMIO configuration option so as to rather than making the choice
for the I/O address space to use at build time for all the adapters
installed in the system let the driver choose the most suitable address
space dynamically on a case-by-case basis at run time.  Make MMIO the
default and resort to port I/O should the default fail for some reason.

This way multiple adapters installed in one system can use different I/O
address spaces each, in particular in the presence of DEFEA adapters in
a pure-EISA or a mixed EISA/PCI system (it is expected that DEFPA boards
will use MMIO in normal circumstances).

The choice of the I/O address space to use continues being reported by
the driver on startup, e.g.:

eisa 00:05: EISA: slot 5: DEC3002 detected
defxx: v1.12 2021/03/10  Lawrence V. Stefani and others
00:05: DEFEA at I/O addr = 0x5000, IRQ = 10, Hardware addr = 00-00-f8-c8-b3-b6
00:05: registered as fddi0

and:

defxx: v1.12 2021/03/10  Lawrence V. Stefani and others
0031:02:04.0: DEFPA at MMIO addr = 0x620c080020000, IRQ = 57, Hardware addr = 00-60-6d-93-91-98
0031:02:04.0: registered as fddi0

and:

defxx: v1.12 2021/03/10  Lawrence V. Stefani and others
tc2: DEFTA at MMIO addr = 0x1f100000, IRQ = 21, Hardware addr = 08-00-2b-b0-8b-1e
tc2: registered as fddi0

so there is no need to add further information.

The change is supposed to cause a negligible performance hit as I/O
accessors will now have code executed conditionally at run time.

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

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