BL1: Add an API for stateless access to noise source

Such stateless API is suitable for usage in pre-main where
global variables are not setup yet and for variables that
do not require cryptographic-quality randomness.

Signed-off-by: Antonio de Angelis <antonio.deangelis@arm.com>
Change-Id: I247247dbfdfc826ef654df46b40a4b1c5b8b0277
3 files changed