plat: imx8m: refactor the code to make it reusable

for the i.MX8M SOCs, part of the code for gpc
and PSCI implementation can be reused and make it
common for all these SoCs. this patch extracts
the common part for reuse.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
9 files changed