linker: update posix linker template, linker.ld

The function `zephyr_linker_sources()` states:
> When placing into NOINIT, RWDATA, RODATA, ROM_START, the contents of
> the files will be placed inside an output section, so assume the
> section definition is already present.

However, in the posix linker.ld template the NOINIT, RWDATA, RODATA, and
ROM_START was not placed inside a pre-defined output section, which
means that linker scripts created for native_posix when
`zephyr_linker_sources()` is used are invalid

This result in the following failure:
> /usr/bin/ld:zephyr/linker_zephyr_prebuilt.cmd:81: syntax error
> collect2: error: ld returned 1 exit status

This PR fixes this issue be predefining output sections according to
the documented behavior.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>