arm64: imx: Fix build error without CONFIG_SOC_BUS

During randconfig builds, I occasionally run into an invalid configuration

drivers/soc/imx/soc-imx8.o: In function `imx8_soc_init':
soc-imx8.c:(.init.text+0x144): undefined reference to `soc_device_register'

while CONFIG_SOC_BUS is not set, the building failed like this. This patch
selects SOC_BUS to fix it.

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: a7e26f35 ("soc: imx: Add generic i.MX8 SoC driver")
Suggested-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>