sparc: move select of ARCH_SUPPORTS_MSI

It is counter intuitive to have the select listed
as part of the PCI option.
Move the select to the SPARC64 specific part of the config.

PCI_MSI has a dependency on PCI so it does not harm to have
it always selected.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>