Bluetooth: controller: Fix BT_CTLR_DEBUG_PINS Kconfig help text

Help text for BT_CTLR_DEBUG_PINS incorrectly mentioned
specific GPIO pins being reserved for this feature, but in
reality the pins reserved vary on the SoC selected, hence
any specific mention of pin details is removed from help
text.

Fixes: #5499

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