caam: Fix CAAM error on startup

caam: Fix CAAM error on startup

In rare cases U-Boot returns an error message when intantiating the RNG
of the CAAM device:
“SEC0:  RNG4 SH0 instantiation failed with error 0xffffffff”
This  means, that even when the CAAM device reports a finished
descriptor, none is found in the output ring.
This might be caused by a missing cache invalidation before
reading the memory of the output ring
This patch moves the cache invalidation of the output ring from start of
the job to immediately after the notification from hardware where the
output ring will be read.

Signed-off-by: Olaf Baehring <olaf.baehring@draeger.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>