build: Set ccache base to build top

This enables ccache sharing between different build tree paths.

Change-Id: I99636bdd2779a6ccf0649f027e35cf67df44b6ae
Don't set CCACHE_BASEDIR if its already set

 * enable use of shared ccache

Change-Id: Ic708a5d5169291d674b167aa2c87bf2c8adaafae
qcom_utils: Make "is-vendor-board-platform,XX" depend on BOARD_HAS_XX_HARDWARE

Prevent qc's code from wrongly kicking in for AOSP-derived
configurations
Edify: Add AssertSomeBaseband

Allow releasetools.py to assert a baseband version. Works just like
AssertSomeBootloader.

Change-Id: Ic8eb341cef1d777d983be25ba21a3bc545819c29