Bluetooth: btqca: Add support to read FW build version for WCN3991 BTSoC

Add support to read FW build version from debugfs node.
This info can be read from
/sys/kernel/debug/bluetooth/hci0/firmware_info

Signed-off-by: Venkata Lakshmi Narayana Gubba <gubbaven@codeaurora.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>