Revise the memory model so that physical memory only supports word level access.

[llee454]

Currently the physical memory device supports byte level accesses (see line 36 in ProcKami/Devices/PMemDevice.v).

• Revise ProcKami/Devices/PMemDevice.v so that the physical memory device only supports word level accesses.
• Revise memDeviceSendReqFn and memDeviceGetResFn so that these functions look at the PMAs to determine whether or not the selected device only supports word level accesses and modifies the values read and written so that they only affect the appropriate memory bits.