If mboot is built with support for packing (signing/encryption) it needs up
to 32KiB. So for simplicity increase the mboot region to 32KiB
unconditionally for WB55 boards (custom WB55 board configurations can still
provide their own linker scripts to override this).
- Split tables and buffers into SRAM2A/2B.
- Use structs rather than word offsets to access tables.
- Use FLASH_IPCCDBA register value rather than option bytes directly.
