Change the logic for allocating user heap for PROTECTED_BUILD:
- Don't rely on SRAM1_END alignment
- Make better use of MPU subregions when allocating the heap
- Don't duplicate the calculation of user heap start in kernel heap
allocation; use the previous calculation directly
Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>
3f6bb76e01