powerpcspe: make GEOM_LABEL kernel built-in

Make powerpspe kernel config in sync with other targets making
GEOM_LABEL built-in to allow use of labels when mounting partitions.

MFC after: 2 days
Sponsored by: Instituto de Pesquisas Eldorado (eldorado.org.br)

(cherry picked from commit 8b57548e9a38ffbb122947043bafabb92b037fb3)