Move the SPICE caps validation from qemuBuildGraphicsSPICECommandLine()
to a new function called qemuDomainDeviceDefValidateSPICEGraphics().
This function is called by qemuDomainDeviceDefValidateGraphics(),
which in turn is called by qemuDomainDefValidate(), validating the graphics
parameters in domain define time.

This validation move exposed a flaw in the 'default-video-type' tests
for PPC64, AARCH64 and s390 archs. The XML was considering 'spice' as
the default video type, which isn't true for those architectures.
This was flying under the radar until now because the SPICE validation
was being made in 'virsh start' time, while the XML validation done in
qemuxml2xmltest.c considers define time.

All other tests were adapted to consider SPICE validation in this
earlier stage.
Reviewed-by: NCole Robinson <crobinso@redhat.com>
Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>