This patch makes the dm relocatable to an arbitrary base address.

Created by: msfschaffner

The last 12bits need to be zero however.

See also https://github.com/msfschaffner/riscv-fesvr/commit/c3a6e8b67c7d6e9c0246186f91c30e5a6f921592 for the required mods in FESVR.

The changes in FESVR and the DM are both backwards compatible in case the DM address base is set to 0x0.