Implement random number generator with hardware support

[nfbot]

From nf-interpreter created by josesimoes : nanoframework/nf-interpreter#307

This can be accomplished in the targets that have a random number generator in hardware.
Has to provide the 'strong' implementation of the class CLR_RT_Random in CLR Core, marked with 'weak' attribute.

[networkfusion]

this could be implemented in a very similar way to the recent CRC32 code...

[josesimoes]

Yeap. That's the plan from the beginning. 😉
Ideally the current code should be replaced with a call to the hardware unit and default to NewlibC implementation when that isn't available.