drm/xe: Add proper detection of the SR-IOV PF mode

SR-IOV PF mode detection is based on PCI capability as reported by
the PCI dev_is_pf() function and additionally on 'max_vfs' module
parameter which could be also used to disable PF capability even
if SR-IOV PF capability is reported by the hardware.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240404154431.583-3-michal.wajdeczko@intel.com