m7: Underp BT tethering

Change-Id: Ia3e028a068ab75f35463721c483b0ca4a3f00b16
m7: Fix Bluetooth sleep bugs

 * Switch to HTC's ioctl interface
 * Set polarity to low
 * Enable two stopbits for serial device

Change-Id: I69f4d60c8cb57437d455ce8fd7651f422d048a30