ARM: imx8m: verdin-imx8mm: Drop bogus content from spl_board_init()

ARM: imx8m: verdin-imx8mm: Drop bogus content from spl_board_init()

The current implementation of spl_board_init() USB boot handling 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>