Not possible to write beyond 16MB using flash sample on FRDM_RW612

[danieldegrasse]

Describe the bug
It is currently not possible to write beyond 16MB of address space using the flash shell sample on the FRDM_RW612, despite the flash chip being 64MB. Note that this is fixed on main by #80261, but is still an issue on Zephyr 3.7

Please also mention any information which could help others to understand
the problem you're facing:

• What target platform are you using? frdm_rw612

To Reproduce
Steps to reproduce the behavior:

1. west build -p always -b frdm_rw612 samples/drivers/flash_shell
2. west flash
3. Attempt to read or write to address beyond 0xFFFFFF
4. Reads will return 0x0, writes will fail silently (or report verification errors)

Expected behavior
Flash writes should not fail beyond 8MB

Impact
MCUBoot support may be affected, otherwise applications using the flash will be limited to 16MB.

[danieldegrasse]

Closing issue, as relevant PR has merged