Provide descriptions for the functions invoking the EFI_RNG_PROTOCOL.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Link: https://lore.kernel.org/r/20200221114716.4372-1-xypron.glpk@gmx.de


Signed-off-by: Ard Biesheuvel <ardb@kernel.org>