stm32f7: configure mpu valid for f7 family

This configuration should be valid for all F7 family devices in general.
Here is the regions info:

	- Region0 : 4GB	  : cacheable & executable.
	- Region1 : 512MB : text area	: strogly ordered & executable.
	- Region2 : 512MB : peripherals : device memory & non-executable.
	- Region3 : 512MB : peripherals : device memory & non-executable.
	- Region4 : 512MB : cortexM area: strongly ordered & non-executable.

Higher region number overrides the lower region configuration.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>