[ARM] orion5x: add sram support for crypto

The security accelerator which can act as a puppet player for the crypto
engine requires its commands in the sram. This patch adds support for the
phys mapping and creates a platform device for the actual driver.

[ nico: renamed device name from "mv,orion5x-crypto" to "mv_crypto"
  so to match the module name and be more generic for Kirkwood use ]

Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Nicolas Pitre <nico@marvell.com>