linker: Fix handling of log_backend iterable section

The log_backed section is now using the iterable section macros so
we should be using zephyr_iterable_section() in common-rom.cmake
so the generation of the linker script is correct for arm clang
compiles.

Fixes #56440

Signed-off-by: Kumar Gala <kumar.gala@intel.com>
(cherry picked from commit 9a77f3d4)