Bluetooth: BR: Support limited discoverable mode

Add a Kconfig BT_LIMITED_DISCOVERABLE_DURATION to set the timeout for
limited discoverable mode.

Add a argument `limited` to function `bt_br_set_discoverable()` to
support the limited discoverable mode.
When enabling discoverable mode with `limited` is true, both write
LIAC and GIAC to controller and set the bit 13 of COD in function
`bt_br_set_discoverable()`. And start a delay worker with the timeout
CONFIG_BT_LIMITED_DISCOVERABLE_DURATION to disable the discoverable
mode.
When disabling discoverable mode, only set GIAC to controller and
clear bit 13 of COD.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>