qemuBuildTPMDevStr() does TPM model validation that can be moved to
qemu_domain.c, allowing validation in domain define time. This patch
moves it to the existing qemuDomainDeviceDefValidateTPM() function.
Reviewed-by: NCole Robinson <crobinso@redhat.com>
Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>