am33xx: Add am33xx_spl_board_init function, call

We need to allow for a further call-out in spl_board_init.  Call this
am33xx_spl_board_init and add a __weak version.  This function may be
used to scale the MPU frequency up, depending on board needs.

Signed-off-by: Tom Rini <trini@ti.com>
3 files changed