west.yml: MCUboot synchronization from upstream

Update Zephyr fork of MCUboot to revision:
  3a195f2207d5eadf45a5c989a870e91aff020d86

Brings following Zephyr relevant fixes:
  - 3a195f22 boot: bootutil: loader: Fix issue with using
    pointers
  - cc7b97be boot: boot_serial: Fix wrong usage of slot numbers
  - 30109df3 boot: bootutil: loader: Fix slot info for
    directXIP/RAM load
  - 7f3c77e1 boot: bootutil: Add write block size checking
  - c40d237a boot: zephyr: Add check for unexpected flash sector
    size
  - f9fc5918 boot: zephyr: Remove broken target config header
    feature
  - f8d8004e boot: zephyr: Allow disabling NRFX_WDT on nRF devices
  - fe26c289 boot: zephyr: boards: nxp: clean .conf files
  - b553290f Add Conexio Stratus Pro board configuration for DFU
  - 41df52e6 boot: SHA512 verification
  - 75672000 cmake: zephyr: change ERROR into FATAL_ERROR

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>