drm/xe: implement driver initiated function-reset

Driver initiated function-reset (FLR) is the highest level of reset
that we can trigger from within the driver. In contrast to PCI FLR it
doesn't require re-enumeration of PCI BAR. It can be useful in case
GT fails to reset. It is also the only way to trigger GSC reset from
the driver and can be used in future addition of GSC support.

v2:
  - use regs from xe_regs.h
  - move the flag to xe.mmio
  - call flr only on root gt
  - use BIOS protection check
  - copy/paste comments from i915
v3:
  - flr code moved to xe_device.c
v4:
  - needs_flr_on_fini moved to xe_device

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>