pmap_mapdev: Consistently use vm_paddr_t for the first argument.

The devmap variants used vm_offset_t for some reason, and a few places
explicitly cast bus addresses to vm_offset_t. (Probably those casts
along with similar casts for vm_size_t should just be removed and
instead permit the compiler to DTRT.)

Reviewed by: markj
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D35961