random: Add syscalls for random subsystem

Create syscalls to make possible using random APIs from user mode
threads. These APIs can have different implementations, like using
entropy driver or Xoroshiro128. Some of these implementations also have
some globals to preserve state between calls.

Make it run entire in user space would require user adding these globals
to their memeory domains and/or grant access to entropy device. Syscalls
simplify its usage.

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>