core: arm: imx: fix imx6solo boot
core: arm: imx: fix imx6solo boot

i.MX6SOLO is almost same with i.MX6DualLite, with difference that
6S has one cpu core, but DualLite has two cpu cores.
i.MX6Solo also needs a9_plat_init.S and imx6.c for basic initialization.

Signed-off-by: Peng Fan <d3c162a96b7fb54e5d94bc77bc2c7cbbce10806f@nxp.com>
Acked-by: Jens Wiklander <7706914404370d7502c27a0eff493dcf491feb51@linaro.org>

pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os