boards: beagle: beagleconnect_freedom: Resize mcuboot partitions

- MCUboot seems to work fine with 40K partition. However, it seems like
  swap using scratch algorithm does not work when slot partition size is
  not a multiple of scratch partition size. So made this partition 56K.
- Tested using samples/subsys/mgmt/mcumgr/smp_svr
- Only uses a bit over 32K. Since flash sector size is 8K, 40K partition
  seems to be a good choice with decent headroom.
- The final partition is as follows:
  - MCUboot: 56K
  - slot0: 640K
  - slot1: 640K
  - scratch 128K

Signed-off-by: Ayush Singh <ayush@beagleboard.org>