libbt-hci: include bdroid_buildcfg.h from device repo

This lets device repos override some constants with their bdroid_buildcfg.h if
necessary.

This fixes Bluetooth issues (namely tethering) on endeavoru where
BTHC_USERIAL_READ_MEM_SIZE needs to be set to a higher value.

Change-Id: I8955963cdb2b34f1ba63f8160861699f7284814f
a2dp hw: adding min freq boost for a2dp through bdroid_localcfg

Adding a simple line into your device tree's bdroid_buildcfg
elevates minfreq of the cpu governor while a2dp is being used.
This helps on some of the devices (like endeavoru) to use
a proper lowest frequency for decoding/encoding of the stream
going on in a2dp usage. It will let the min freq revert when
a2dp is finished. If the #define is not added the code is not
compiled in. The whole thing is added to this part (a2dp)
only, because other bluetooth operations doesnt need the
elevation of the min freq generally.

Example: in device's bdroid_buildcfg.h
 define A2DP_ENFORCE_MIN_FREQ "204000"

Change-Id: I2cd94e626eb2a6d04a6e52ddac94fa5773eb09d8
Revert "Update btif_media_task.c"

This reverts commit 6778bf52d13a1a7c3aa930d305ee52bcd9c4e147.