west.yml: MCUboot synchronization from upstream

Update Zephyr fork of MCUboot to revision:
  47b34362552835621bc289d53d2127691088cb7c

Brings following Zephyr relevant fixes:
 - 47b34362 zephyr: kconfig: Prevent MBEDTLS selection when
   tinycrypt is used
 - cd82f8bf boot: zephyr: add support for lpcxpresso55s28

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