sif: epsc: For Xen dom0 configure resources for all 32 VFs at driver load

sif: epsc: For Xen dom0 configure resources for all 32 VFs at driver load

As of EPSC API version 2.9 firmware can distribute resources based on
the number of PCI functions the PF driver requests support for.
Older firmware will just ignore the value.

This commit enforces no VFs configured as the default setting
but enable all 32 VFs if a Xen PV domain is detected.

To allow overriding this behaviour we add a new module parameter
vf_max which can be used to override the number of VFs configured
for instance for use with other virtualization engines than Xen
and for debugging/tuning purposes. The vf_max parameter takes the
following values:

-2:  Use NVRAM configured firmware defaults (backward compat mode)
-1  (now default) : Exadata mode as described above
0-32:  Configure explicitly for that many VFs (only selected values
     are supported by firmware)

Orabug: 24424521

Signed-off-by: Knut Omang <knut.omang@oracle.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>