Factored common MPU code from different architectures

miosix/arch/common/drivers/memory_protection.h

miosix/arch/common/drivers/mpu_stm32.cpp

miosix/arch/common/drivers/mpu_stm32.h

...h/cortexM3_stm32f2/common/interfaces-impl/portability.cpp

...ortexM3_stm32f2/common/interfaces-impl/portability_impl.h

...h/cortexM4_stm32f4/common/interfaces-impl/portability.cpp

...ortexM4_stm32f4/common/interfaces-impl/portability_impl.h

...h/cortexM7_stm32f7/common/interfaces-impl/portability.cpp

...ortexM7_stm32f7/common/interfaces-impl/portability_impl.h

miosix/config/Makefile.inc

miosix/interfaces/portability.h

miosix/kernel/kernel.cpp

miosix/kernel/process.cpp

miosix/kernel/process.h

miosix/kernel/scheduler/control/control_scheduler.cpp

miosix/kernel/scheduler/edf/edf_scheduler.cpp

miosix/kernel/scheduler/priority/priority_scheduler.cpp