Add ld/st priv mode, sum & PMP iface signals to acc_dispatcher

Created by: michael-platzer

Hi, this PR adds 4 additional ports for the current load/store privilege mode, the current content of the sum field of the mstatus CSR, and the contents of the PMP configuration and address CSRs to the acc_dispatcher.

These signals are necessary to perform memory protection checks on memory requests originating from an accelerator in a custom implementation of the acc_dispatcher module. Those signals allow to determine the privilege mode of loads and stores performed by an accelerator and, for example, to add an instance of the pmp module to enforce the current physical memory protection rules on those requests.

This PR simply adds the necessary ports and connects the corresponding signals to the acc_dispatcher module. The protection checks that they enable need to be added to a custom implementation of the acc_dispatcher which interfaces with the respective accelerator.

CC @domenicw @zarubaf