power: sequencing: qcom-wcn: Report power controllability

The "bluetooth" and "wlan" targets drive the BT_EN and WLAN_EN GPIOs to
gate the respective functions. These GPIOs are optional, on some boards
they are hardwired to an always-on pull-up and not routed to a host GPIO.
In that case the corresponding enable/disable callbacks are no-ops, so the
consumer cannot gate or reset that function on its own.

Implement the .is_controllable() callback on the "bluetooth" and "wlan"
targets so that consumers can query this via the pwrseq API.

Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Link: https://patch.msgid.link/20260904-monza-wireless-v6-5-d8c5042b3efd@oss.qualcomm.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>