random: Include header where it is used

Unit tests were failing to build because random header was
included by kernel_includes.h. The problem is that rand32.h
includes a generated file that is either not generated or not
included when building unit tests. Also, it is better to limit
the scope of this file to where it is used.

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