manifest: Update sdk-mcuboot

Updates MCUboot to include support for encrypted compressed images
and removes restriction for single image

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

Author: nordicjm

west.yml

@@ -130,7 +130,7 @@ manifest:
           compare-by-default: true
     - name: mcuboot
       repo-path: sdk-mcuboot
-      revision: b82206c15fff357c151c24bf97c99c4348d14a46
+      revision: pull/391/head
       path: bootloader/mcuboot
     - name: qcbor
       url: https://github.com/laurencelundblade/QCBOR