audioflinger: increase client heap size to 2MB

- Playback of 24 bit 192kHz clips fails during device switch
between wired headset and BT when repeat track is enabled.
- Memory allocation for AudioTrack fails because the heap gets
fragmented and free chunks of the size requested are not available.
- Increase the current heap size to 2MB to ensure that there is
always a free chunk to accommodate the requested size.

CRs-Fixed: 855910
Change-Id: I2eb18b15557fa264fb66ff282746cad4e6c718f7