net: enetc: deny offload of tc-based TSN features on VF interfaces

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

net: enetc: deny offload of tc-based TSN features on VF interfaces

TSN features on the ENETC (taprio, cbs, gate, police) are configured
through a mix of command BD ring messages and port registers:
enetc_port_rd(), enetc_port_wr().

Port registers are a region of the ENETC memory map which are only
accessible from the PCIe Physical Function. They are not accessible from
the Virtual Functions.

Moreover, attempting to access these registers crashes the kernel:

$ echo 1 > /sys/bus/pci/devices/0000\:00\:00.0/sriov_numvfs
pci 0000:00:01.0: [1957:ef00] type 00 class 0x020001
fsl_enetc_vf 0000:00:01.0: Adding to iommu group 15
fsl_enetc_vf 0000:00:01.0: enabling device (0000 -> 0002)
fsl_enetc_vf 0000:00:01.0 eno0vf0: renamed from eth0
$ tc qdisc replace dev eno0vf0 root taprio num_tc 8 map 0 1 2 3 4 5 6 7 \
queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 base-time 0 \
sched-entry S 0x7f 900000 sched-entry S 0x80 100000 flags 0x2
Unable to handle kernel paging request at virtual address ffff800009551a08
Internal error: Oops: 96000007 [#1] PREEMPT SMP
pc : enetc_setup_tc_taprio+0x170/0x47c
lr : enetc_setup_tc_taprio+0x16c/0x47c
Call trace:
enetc_setup_tc_taprio+0x170/0x47c
enetc_setup_tc+0x38/0x2dc
taprio_change+0x43c/0x970
taprio_init+0x188/0x1e0
qdisc_create+0x114/0x470
tc_modify_qdisc+0x1fc/0x6c0
rtnetlink_rcv_msg+0x12c/0x390

Split enetc_setup_tc() into separate functions for the PF and for the
VF drivers. Also remove enetc_qos.o from being included into
enetc-vf.ko, since it serves absolutely no purpose there.