arm: omap: Detect boot mode very early

ROM stores the boot params information in a known location
and passes it to SPL. This information needs to be copied
very early during boot or else there is a chance of getting
corrupted by SPL. So move this boot device detection very early
during boot.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>