include/zephyr: Use ROMABLE_REGION for LMA in .last_ram_section

Currently RAMABLE_REGION is used for both virtual address (VMA)
and a load address (LMA). It results in wrong LMA for some platforms.
This commits adds using ROMABLE_REGION for LMA.

Signed-off-by: Franciszek Pindel <fpindel@antmicro.com>