ARM: dts: imx: Remove optional 'fsl,sec-era' property

Since commit 654f2b93 ("crypto: caam - allow retrieving 'era' from
register") the CAAM driver is capable of obtaining the era version by
reading the appropriate CAAM registers, so let the CAAM driver discover
the era version in run-time instead of hardcoding such information in the
device tree.

According to Documentation/devicetree/bindings/crypto/fsl-sec4.txt the
'fsl,sec-era' is an optional property and this can be safely removed
now.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>