scripts: emit enum parameters in API build description

scripts: emit enum parameters in API build description

Currently the information about enums in the API document lacks any
mention of parameters, so it is impossible to tell what kind of enum
declaration is present in the libvirt API header. With this change

  <macro name='LIBVIR_CHECK_VERSION' file='libvirt-common'>
  <macro name='VIR_COPY_CPUMAP' file='libvirt-domain'>
  ...snip...

becomes

  <macro name='LIBVIR_CHECK_VERSION' file='libvirt-common' params='major,minor,micro'>
  <macro name='VIR_COPY_CPUMAP' file='libvirt-domain' params='cpumaps,maplen,vcpu,cpumap'>
  ...snip...

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>