Correct the memory rman ranges to be to BUS_SPACE_MAXADDR

Summary:
As part of the migration of rman_res_t to be typed to uintmax_t, memory ranges
must be clamped appropriately for the bus, to prevent completely bogus addresses
from being used.

This is extracted from D4544.

Reviewed By: cem
Sponsored by: Alex Perez/Inertial Computing
Differential Revision: https://reviews.freebsd.org/D5134