Revert "cmake: linker: arm: put RAM sections in RAM region"

This reverts commit f5eada55.

Fixes #57590.

In order to fix incorrect program headers with CMAKE_LINKER_GENERATOR,
issue #59064 needs to be addressed first. Until then, revert to the
status quo from several versions back.

Signed-off-by: Grzegorz Swiderski <grzegorz.swiderski@nordicsemi.no>