Bluetooth: MGMT: Add initial implementation of MGMT_OP_HCI_CMD_SYNC

This adds the initial implementation of MGMT_OP_HCI_CMD_SYNC as
documented in mgmt-api (BlueZ tree):

Send HCI command and wait for event Command
===========================================

	Command Code:		0x005B
	Controller Index:	<controller id>
	Command Parameters:	Opcode (2 Octets)
				Event (1 Octet)
				Timeout (1 Octet)
				Parameter Length (2 Octets)
				Parameter (variable)
	Return Parameters:	Response (1-variable Octets)

	This command may be used to send a HCI command and wait for an
	(optional) event.

	The HCI command is specified by the Opcode, any arbitrary is supported
	including vendor commands, but contrary to the like of
	Raw/User channel it is run as an HCI command send by the kernel
	since it uses its command synchronization thus it is possible to wait
	for a specific event as a response.

	Setting event to 0x00 will cause the command to wait for either
	HCI Command Status or HCI Command Complete.

	Timeout is specified in seconds, setting it to 0 will cause the
	default timeout to be used.

	Possible errors:	Failed
				Invalid Parameters

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>