Build - Automatically set QCOM audio, display, media variants

* Device platform should determing the HAL that ought to be used. This
commit forces QCOM_HARDWARE to select the -caf HAL variants, which
are then broken down by platform within the variant path.

Change-Id: I3d752a7f5a31e695a1e83286bbeb2c03b1e4719d
Signed-off-by: STELIX <ssspinni@gmail.com>