spl: Introduce new function spl_board_prepare_for_boot

Call this function before passing control from SPL.
For fpga case it is necessary to enable for example level shifters
when bitstream is programmed.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
2 files changed