Bluetooth: controller: Fix DEBUG_PINS_CPUAPP dependency

Remove the BT_LL_SW_SPLIT dependency for
BT_CTLR_DEBUG_PINS_CPUAPP when building CPUAPP application
that is using Zephyr BLE HCI controller on the CPUNET core.

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