bhnd_usb: Use bus_generic_rman_*

For SYS_RES_MEMORY, use bus_generic_rman_* for
activate/deactivate_resource methods as well as custom
map/unmap_resource methods that request submappings of the sc_mem
resource allocated from the parent bus.

Differential Revision: https://reviews.freebsd.org/D43938

(cherry picked from commit b25f03a1a27256c8d638a7e82ac3f6248994d5f3)