cmake: linker generator: group symbol from section

The root cause of #38591 was region symbols being placed before the
section description for data region.

Some region start symbols are placed before section description, other
region start symbols are placed inside the first section in the region
and thus identical to the sections own first symbol.

To support both schemes with the linker generator, a new
`SYMBOL SECTION` argument has been added to the zephyr_linker_group()
function.

The ld_script.cmake linker script generator has been updated to support
the new argument so that generated ld linker script has identical
behavior to the templated ld linker scripts.

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