camera: libexif is now libjhead

Fixes undefined reference errors when building jem on 4.4.3.
See also https://github.com/CyanogenMod/android_hardware_ti_omap4xxx/commit/0fbe7ecfb0a526c02b774208fa00e0cba19d13a4

[hashcode0f@gmail.com: re-added libexif with PLATFORM var checks so repo can be used to build 4.4.x still]
Signed-off-by: Hashcode <hashcode0f@gmail.com>

Change-Id: I51ec616010228ae2c9217f47b9a6a243e5b20b3f