arm64: Increase dmap size to 95 TiB
The Ampere Altra has physical memory populated sparsely within the
physical address space. Increase the size of the dmap to cover all
Reviewed by: andrew
Approved by: scottl (implicit)
MFC after: 1 week
Sponsored by: Ampere Computing, Inc.
Differential Revision: https://reviews.freebsd.org/D26134