Move the PM validation being done by qemuBuildPMCommandLine() to
to a new qemuDomainDefValidatePM() function. This new function
is called by qemuDomainDefValidate(), promoting PM validation in
domain define time.

Tests were adapted to consider the new caps being needed in
this earlier stage.
Reviewed-by: NCole Robinson <crobinso@redhat.com>
Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>