CC3XX: Refactor get_random_permutation()

cc3xx_lowlevel_rng_get_random_permutation() always gets its
randomness from the LFSR as it does not require cryptographic
level security for the random number, hence just remove the
option to choose DRBG and always use LFSR.

Signed-off-by: Antonio de Angelis <antonio.deangelis@arm.com>
Change-Id: I9145b35106c2ea9d82ee15ab40f624986c02f38b
8 files changed