mips: octeon: Add cvmx-helper.c

Import cvmx-helper.c from 2013 U-Boot. It will be used by the later
added drivers to support PCIe and networking on the MIPS Octeon II / III
platforms.

Signed-off-by: Aaron Williams <awilliams@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>