west.yml: MCUboot synchronization from upstream

Update Zephyr fork of MCUboot to revision:
  1b2fc096d9a683a7481b13749d01ca8fa78e7afd

Brings following Zephyr relevant fixes:

  - 1b2fc096 boot: Reuse pointers for flash_area objects from state
  - d00b11dc boot: bootutil: Take into account scratch trailer when
    computing max image size
  - d1a3b953 boot: bootutil: Ensure the whole trailer is erased
    when it is large
  - 66d41e73 boot: bootutil: Fix scratch trailer overwritten if
    image trailer is large
  - 8975d5c4 boot: bootutil: Fix underflow in swap-scratch when
    trailer is large
  - a43167e3 zephyr: fix Mbed TLS configuration header file
    selection
  - fbd2267e boot: bootutil: Fix invalid last sector computation
    for swap-scratch
  - 7330df7c boot: bootutil: Fix last sector index computation for
    swap-offset
  - 429e2fea boot: zephyr: kconfig: Add new defaults option for FIH
  - 602cb459 Fix path for DT example
  - 3ff75490 zephyr: Add Kconfig option
    CONFIG_BOOT_KEY_IMPORT_BYPASS_ASN
  - f2b6def9 zephyr: Enable building ed25519 PSA variant with
    Zephyr

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