qemu: Update qemuDomainSupportsPCI()

qemu: Update qemuDomainSupportsPCI()

The sparc architecture doesn't support PCI, and neither do the
isapc and microvm machine types on x86 architectures.

One of the isapc/microvm tests starts failing as a consequence
of this change, which is expected; somewhat surprisingly,
another test for the same machine types goes from an early/hard
failure (PARSE_ERROR) to a late/soft one (FAILURE) instead.
This will be rectified by a later commit.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>