plat: imx8mq: rename files for imx8mq

For the i.MX8 media processor, we have i.MX8MQ and i.MX8MM etc.
so rename the file name of imx8m_bl31_setup.c and imx8m_psci.c
to imx8mq_xxx to make it more clear that these file is specific
to i.MX8MQ.

Signed-off-by: Bai Ping <ping.bai@nxp.com>
(cherry picked from commit 146f4caf3c60fb323db12a4ff3c960c8f08d6f17)

Conflicts:
	plat/imx/imx8mq/platform.mk
3 files changed