arm: mach-k3: copy bootindex to OCRAM for main domain SPL

Texas Instruments has begun enabling security settings on the SoCs it
produces to instruct ROM and TIFS to begin protecting the Security
Management Subsystem (SMS) from other binaries we load into the chip by
default.

One way ROM and TIFS do this is by enabling firewalls to protect the
OCSRAM and HSM RAM regions they're using during bootup.

The HSM RAM the wakeup SPL is in is firewalled by TIFS to protect
itself from the main domain applications. This means the 'bootindex'
value in HSM RAM, left by ROM to indicate if we're using the primary
or secondary boot-method, must be moved to OCSRAM (that TIFS has open
for us) before we make the jump to the main domain so the main domain's
bootloaders can keep access to this information.

Signed-off-by: Bryan Brattlof <bb@ti.com>