soc: xtensa: imx8: Remove include/soc directory

Since platform.h is a SOF-specific header that's no
longer used there's no point in keeping the include/soc directory.
As such, move memory.h to include/ and modify the linker script
to reflect this location change.

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