Build: Change default build option to MinSizeRel

* By default CMake's Release option builds with -O3,
  which isn't efficient for Cortex-M devices,
  where we wanted the lowest ROM/RAM usage.
* If TFM_SYSTEM_PROCESSOR is defined, then build and link
  with this cpu instead of arch with both
  armclang and gcc

Signed-off-by: Dávid Házi <david.hazi@arm.com>
Change-Id: I7550ab435fcf6bb595dcc153665009e47163214b
5 files changed