Move EGL Headless validation from qemuBuildGraphicsEGLHeadlessCommandLine()
to qemuDomainDeviceDefValidateGraphics(). This function is called by
qemuDomainDefValidate(), validating the graphics parameters in domain
define time.
Reviewed-by: NCole Robinson <crobinso@redhat.com>
Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>