arm: omap3: Detect boot mode very early

Fixes 4bd754d8 ("arm: omap: Detect boot mode very early") where
the intent was to store the boot params information in a known
location and pass it to SPL very early. Unfortunately it didn't
account for OMAP3 boards.

This patch adds adds this functionality back into OMAP3 boards.

Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Adam Ford <aford173@gmail.com>