pci_alloc_irq_vectors() is given a min and max vector value.
pci_enable_msi() will always succeed independent on these as it does
not know about them. Further it will only ever allocate 1 "vector"
not supporting any other amount.
So upfront check that (a) the available pci_msi_count() can satisfy the
requested minv and (b) given the pci_enable_msi() hard coded limit check
that minv is not larger than 1.
If we cannot satisfy either requirement return an error.

This fixes problems with drivers which check that the returned value
of allocated "vectors" will match their requests and only otherwise try
to fall back to ask for 1 or deal otherwise.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days