crypto: caam - allow retrieving 'era' from register

The 'era' information can be retrieved from CAAM registers, so
introduce a caam_get_era_from_hw() function that gets it via register
reads in case the 'fsl,sec-era' property is not passed in the device
tree.

This function is based on the U-Boot implementation from
drivers/crypto/fsl/sec.c

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
Tested-by: Breno Lima <breno.lima@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>