soc: imx9: remove custom linker script

The custom linker script was required because SOF needed
some extra linker sections. Other than that, the custom linker
script was identical to the common architecture script. This
commit removes the custom linker script because:

	* keeping the custom linker script in sync with the
	common one is troublesome.

	* application-specific linker sections shouldn't be
	included in the generic soc linker script. Instead,
	they should be handled at the application level
	(i.e: via cmake commands if additional sections are
	needed or via a new, custom linker script if more
	changes are needed)

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