linker: Fix handling of _static_thread_data section

_static_thread_data should be in ROM as its static data.  So move
it from common-ram.cmake to common-rom.cmake and fix it the params
we call zephyr_iterable_section with.

Signed-off-by: Kumar Gala <kumar.gala@intel.com>
(cherry picked from commit 61f9d4ba)