Bluetooth: Add support for Get Clock Info mgmt command

This patch implements support for the Get Clock Information mgmt
command. This is done by performing one or two HCI_Read_Clock commands
and creating the response from the stored values in the hci_dev and
hci_conn structs.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>