memory: mtk-smi: Use platform_register_drivers

In this file, we have 2 drivers, smi-common and smi-larb.
Use platform_register_drivers.

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Link: https://lore.kernel.org/r/20210121062429.26504-2-yong.wu@mediatek.com


Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>