Bluetooth: Controller: Single timer use Extended Scanning nRF54L support

Update Extended Scanning for single timer use support
required for nRF54L Series SoCs.

As the timer is reset on every radio end, use the
radio_tmr_hcto_configure_abs() function to set the header
complete timeout correctly when using single timer for s/w
switching.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>