Create recovery.img as .zip file for uBoot platforms (encore)

This updates the recovery build process for uBoot platforms such as
the encore (NookColor) to build the recovery ramdisk and create a
zip file with both the recovery ramdisk and kernel in it.

This will allow RomManager to push the kernel and ramdisk required
to support ext4 roms without making users manually install the
recovery kernel as they are doing today.

recovery.img is the zip file
ramdisk-recovery.img is the ramdisk

This commit also fixes 'make recoveryimage' which didn't work without
building bacon first.  A bug introduced in I2cf193e8f8bf93edbd25c6057c5c3e6aa90e7f77

Change-Id: Ia199de6f33c776698ce5a5972958867c9f7f3637