[GSoC] libmm project updates

* Setup RTEM environment for libmm. This action includes :

• libmm score API.
• libcpu/mm.h Header file to serve as an interface for low-level libmm API.
• Stubs for BSPs that do not implement libmm.
• mmtest1 test case.
•  Changes to all BSPs Makefiles to accommodate former files.

* libmm MPU implementation (not tested) : A simple implementation  that wraps ARMv7 MPU API.

* Change API prototypes and delete MME struct. Now low-level API takes base, size, attributes as args instead of MME struct pointer. 

* Adjust the current ARM MMU code and integrate it into Raspberry PI BSP (built successfully). The code is to be tested/debugged once I get the USB/TTL cable.