WORKAROUND: QCLINUX: Bluetooth: support Bluetooth over both USB and UART

[shuaz-shuai]

On Hamoa boards, a single M.2 slot may host either a UART-based Bluetooth card or a USB-based Bluetooth card. As a result, the UART controller node is always present in the device tree, while the USB Bluetooth path is hot‑pluggable.

When Bluetooth is actually used over USB, the hci_qca UART driver still probes due to the DT node being present. During probe/power sequencing it drive BT_EN low (either directly or via the WCN power sequencer), which can cut power to the shared Bluetooth device and cause the USB Bluetooth interface to disconnect.

Model BT_EN as an always-on fixed regulator and ensure the UART path does not claim power control when BT_EN is not described for that consumer:
- Describe BT_EN as a fixed regulator (GPIO 116) that is boot-on and
always-on, so it cannot be inadvertently deasserted by the UART probe.
- Remove bt-enable-gpios from the WCN7850 power sequencer node and drop
its BT pinctrl entry.
- Wire the bluetooth DT supplies to the always-on 3.3V rail so the UART
driver can acquire its regulators without depending on the WCN PMU
regulators in this dual-path configuration.
- Treat WCN7850 like WCN6750/WCN6855 in hci_qca: if no bt_en GPIO is
provided for the UART device, disable power control for that instance.
- In pwrseq-qcom-wcn, do not match a "bluetooth" consumer if the
sequencer has no bt-enable GPIO configured. This prevents the sequencer
from binding to a bluetooth consumer node in the "BT_EN tied high /
absent from DT" case and allows the consumer to fall back accordingly.

With these changes, probing the UART path no longer deasserts BT_EN when Bluetooth is operating over USB, avoiding unexpected USB disconnects.

Without this change, Bluetooth over USB does not work.
This is a temporary workaround. Once a proper M.2 binding or solution is upstreamed, both the DTS and driver changes will be reworked and re-submitted according to the M.2 model.

CRs-Fixed: 4480880

[shashim-quic]

QCLINUX: Bluetooth: support Bluetooth over both USB and UART
This is a temporary workaround. Once a proper M.2 binding or solution is upstreamed, both the DTS and driver changes will be reworked and re-submitted according to the M.2 model.

Please prefix it with WORKAROUND , it is so.

[shuaz-shuai]

QCLINUX: Bluetooth: support Bluetooth over both USB and UART
This is a temporary workaround. Once a proper M.2 binding or solution is upstreamed, both the DTS and driver changes will be reworked and re-submitted according to the M.2 model.

Please prefix it with WORKAROUND , it is so.

The prefix has been added. Please help review.

[sgaud-quic]

Please fix Compilation Issue :
/opt/actions-runner/_work/kernel-config/kernel-config/arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts:473.38-488.4: ERROR (phandle_references): /regulator-wcn-bt-en: Reference to non-existent node or label "wcn_bt_en"

https://github.com/qualcomm-linux/kernel-config/actions/runs/23594157895/job/68706519199