ARM: imx8m: phycore_imx8mm: Drop bogus spl_board_init()

ARM: imx8m: phycore_imx8mm: Drop bogus spl_board_init()

The current implementation of spl_board_init() is not correct,
the MX8MM BootROM v1 does not support SDP load when re-entered
from U-Boot SPL, it is up to U-Boot to perform the next stage
load using its own internal CI gadget driver and SDP protocol
implementation. Drop the spl_board_init() to let SPL continue
with normal load in case the SDP support is enabled.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Peng Fan <peng.fan@nxp.com>