powerpc/pseries: Honor the generic "no_64bit_msi" flag

commit 415072a041bf50dbd6d56934ffc0cbbe14c97be8 upstream.

Instead of the arch specific quirk which we are deprecating

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>