Allow devices to specify certain ro. props via TARGET_UNIFIED_DEVICE

This modifies buildinfo.sh to not set model, name, description, and
fingerprint in build.prop. These can then be set via custom init
lib.
This also fixes ota_from_target_files to function without these
props being preset.

Change-Id: I945b2c38e60b207d2d0f82b34f4f230ac21b0657
Merge branch 'cm-11.0' of github.com:CyanogenMod/android_build into tfkk-4.4

Conflicts:
	core/Makefile

Change-Id: I48f2b73d830b51235a6dfdbde6cbac4fab43f4e6