util: hostmem: Make parameters for 'virHostMemSetParameters' introspectable

util: hostmem: Make parameters for 'virHostMemSetParameters' introspectable

Refactor the validation using 'virTypedParamsValidateTemplate' and
export the template so that 'qemuNodeSetMemoryParameters' can expose
them via introspection.

In addition since 'virHostMemSetParameters' is conditionally compiled,
platforms which don't support it will not expose given params.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>