soc: xtensa: imx8: Configuration cleanup

As the name suggests, this commit attempts to cleanup some
of the configurations for the i.MX8 series. This cleanup
consists of either relocating the configuration or removing
unnecessary configurations.

As a rule of thumb, SoC-specific configurations have been moved
to Kconfig.series. If the configuration is by default 'y' and
needs to be set to 'n' or it has a numeric value then it has
been moved to Kconfig.defconfig.series. Configurations that
are default 'n' and were also explicitly set to 'n' have been
removed. Also, enabling logging has been moved to the board
level to avoid having to force all boards based on the same
SoC to enable logging.

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>