Pues como no te coja esto, (esta me ha funcionado a mi)
Código:
(select country, count(provider_id)as total
from provider group by country order by total DESC Limit 5)
UNION
(Select 'otros' as country, count(provider_id) as total from provider where not EXISTS (select country, count(provider_id)as total
from provider group by country order by total DESC Limit 5))