Bluetooth: Controller: Add Kconfig to enable CTE RX in conn mode

The CTE reception and sampling in connected mode was enabled
with CONFIG_BT_CTLR_DF_CONN_CTE_REQ. This is a separate fearure
tha can be enabled when CTE reqest procedure is disabled.
What more the CONFIG_BT_CTLR_DF_CONN_CTE_REQ is dependent
on CONFIG_BT_CTLR_DF_CONN_CTE_RX, not other way around.

The commit adds separate Kconfig to provide such possibility.
Also changes compilation guards for code related with the
CTE reception and sampling.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>