drm/xe/vf: Don't expose sysfs attributes not applicable for VFs

In the Linux kernel, the following vulnerability has been resolved:

drm/xe/vf: Don't expose sysfs attributes not applicable for VFs

VFs can't read BMG_PCIE_CAP(0x138340) register nor access PCODE
(already guarded by the info.skip_pcode flag) so we shouldn't
expose attributes that require any of them to avoid errors like:

[] xe 0000:03:00.1: [drm] Tile0: GT0: VF is trying to read an \
inaccessible register 0x138340+0x0
[] RIP: 0010:xe_gt_sriov_vf_read32+0x6c2/0x9a0 [xe]
[] Call Trace:
[] xe_mmio_read32+0x110/0x280 [xe]
[] auto_link_downgrade_capable_show+0x2e/0x70 [xe]
[] dev_attr_show+0x1a/0x70
[] sysfs_kf_seq_show+0xaa/0x120
[] kernfs_seq_show+0x41/0x60

(cherry picked from commit a2d6223d224f333f705ed8495bf8bebfbc585c35)