arm64: random: implement arch_get_random_int/_long based on RNDR

arm64: random: implement arch_get_random_int/_long based on RNDR

When support for RNDR/RNDRRS was introduced, we elected to only
implement arch_get_random_seed_int/_long(), and back them by RNDR
instead of RNDRRS. This was needed to prevent potential performance
and/or starvation issues resulting from the fact that the /dev/random
driver used to invoke these routines on various hot paths.

These issues have all been addressed now [0] [1], and so we can wire up
this API more straight-forwardly:

- map arch_get_random_int/_long() onto RNDR, which returns the output of
  a DRBG that is reseeded at an implemented defined rate;
- map arch_get_random_seed_int/_long() onto the TRNG firmware service,
  which returns true, conditioned entropy, or onto RNDRRS if the TRNG
  service is unavailable, which returns the output of a DRBG that is
  reseeded every time it is used.

[0] 390596c9959c random: avoid arch_get_random_seed_long() when collecting IRQ randomness
[1] 2ee25b6968b1 random: avoid superfluous call to RDRAND in CRNG extraction

Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220113131239.1610455-1-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>