scripts/mkstandalone: fix quoting

Spaces in an argument made the quoted result occupy multiple array
fields after splitting.  The test broke if the third argument was
shifted because of that.  (arm/gicv2*)

Populate the array explicitly, instead of relying on splitting.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Message-Id: <20170726083909.30029-1-rkrcmar@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>