imx: imx9: Imply CPU_IMX by default

imx: imx9: Imply CPU_IMX by default

The imx8_cpu driver is a CPU Driver that supports the i.MX9
family to display the CPU type, temperature grade and
current operating temperature.  The older file,
arch/arm/mach-imx/cpu.c, does not support i.MX9, so this config
is enabled in various IMX9 boards.  Instead of having this option
enabled in every IMX9, select this driver by default for the
platform.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>