board: synquacer: Initialize SCBM SMMU at board_init()

Since the SCBM SMMU is not only connected to the NETSEC
but also shared with the F_SDH30 (eMMC controller), that
should be initialized at board level instead of NETSEC.

Move the SMMU initialization code into board support
and call it from board_init().

Without this fix, if the NETSEC is disabled, the Linux
eMMC ADMA cause an error because SMMU is not initialized.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>