Use device specific gps.conf files & fall back to gps.conf
if $(TARGET_DEVICE) is missing.

Change-Id: I8c1084eab15997d3bc8832a614a9b7face973500
G2: Cleanup & Fixup init.g2.rc & fstab.g2 mounting & permissions

Change-Id: Icd15f45bddd8d03165113e73cc137f06d58e207f
Remove direct call to KERNEL_SOURCE since it isn't used, only
TARGET_KERNEL_TOOLCHAIN_VERSION & TARGET_KERNEL_USE_AOSP_TOOLCHAIN

Change-Id: I9519a08b7defcf368d07b62f9e9bb2e31ce8f4f5