Bluetooth: btintel_pcie: Refactor FLR to use device_reprobe()

The FLR branch in btintel_pcie_reset_work() open-coded the entire
re-init sequence: btintel_pcie_release_hdev() (hci_unregister_dev +
hci_free_dev), pci_try_reset_function(), enable_interrupts /
config_msix / enable_bt / reset_ia / start_rx, then
btintel_pcie_setup_hdev() (hci_alloc_dev_priv + hci_register_dev).
Every probe() init step had to be kept in sync with this second
copy in the reset path, and any failure mid-sequence left state to
unwind by hand.

The PLDR path already delegates teardown and re-init to the PCI
core via device_reprobe(): .remove() destroys data through devres
and unregisters hdev, then .probe() rebuilds everything from
scratch. Apply the same model to FLR.

Introduce btintel_pcie_perform_flr() mirroring perform_pldr(). It
runs pci_try_reset_function() (required to avoid the device_lock
ABBA against btintel_pcie_remove(), which calls
disable_work_sync(&reset_work) while holding device_lock) followed
by device_reprobe(). On success, data is destroyed and a fresh
probe re-INIT_WORKs coredump_work with disable count 0, so
enable_work() must not be called; on failure, data is still alive
and the caller balances the earlier disable_work_sync(). The
contract is documented on the helper and reiterated at the
reset_work() call site.

reset_work() shrinks to interrupt/worker drain, dispatch on
reset_type, and the single asymmetry between the two paths. The
out_enable label, the manual unregister/register pair, and the
forward declaration of btintel_pcie_setup_hdev() are dropped.

No intended functional change; FLR and PLDR now share one
teardown contract.

Fixes: 256ab9520d15 ("Bluetooth: btintel_pcie: Support Function level reset")
Assisted-by: GitHub-Copilot:claude-4.7-opus
Signed-off-by: Kiran K <kiran.k@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>