arm: zynq: Drop unnecessary code in SPL board_init_f()

Move to the new way of starting up SPL. Clearing of BSS and calling
board_init_r() is now handled by crt0.S.

Also tidy up the header include order.

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