docs(maintainers): add maintainers for i.MX9 SoCs

Add maintainers for NXP i.MX9 SoC family.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Change-Id: I6dd694af56da9f4d241fda28b781254586b5f462
1 file changed