unzip: set ENABLE_DESKTOP to allow unpacking signed Android OTAs

Without this flag set, attempting to use BusyBox unzip to unpack a
signed Android OTA results in the error

unzip: zip flags 1 and 8 are not supported

Set ENABLE_DESKTOP for the unzip code to enable the necessary feature.

Change-Id: I3f764bde678311a8d3de787ea503f9cc793337a3
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_external_busybox into temp