crypto: caam - optimize RNG sample size

TRNG "sample size" (the total number of entropy samples that will be taken
during entropy generation) default / POR value is very conservatively
set to 2500.

Let's set it to 512, the same as the caam driver in U-boot
(drivers/crypto/fsl_caam.c) does.

This solves the issue of RNG performance dropping after a suspend/resume
cycle on parts where caam loses power, since the initial U-boot setttings
are lost and kernel does not restore them when resuming.

Note: when changing the sample size, the self-test parameters need to be
updated accordingly.

Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Meenakshi Aggarwal <meenakshi.aggarwal@nxp.com>
Reviewed-by: Gaurav Jain <gaurav.jain@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>