Add pci_vendor, pci_device, pci_class, pci_subclass decoders

[bobrik]

Running the example in a vm:

ivan@vm:~$ sudo lspci
00:00.0 Host bridge: Red Hat, Inc. QEMU PCIe Host bridge
00:01.0 Non-Volatile memory controller: Red Hat, Inc. QEMU NVM Express Controller (rev 02)
00:02.0 Non-Volatile memory controller: Red Hat, Inc. QEMU NVM Express Controller (rev 02)
00:03.0 Unclassified device [0002]: Red Hat, Inc. Virtio filesystem
00:04.0 Unclassified device [0002]: Red Hat, Inc. Virtio filesystem

ivan@vm:~$ curl -s http://localhost:9435/metrics | fgrep pci
ebpf_exporter_build_info{branch="ivan/pci",goarch="arm64",goos="linux",goversion="go1.19.8",revision="072572d",tags="unknown",version="v2.2.0-15-g072572d"} 1
ebpf_exporter_ebpf_program_info{config="pci",id="279",program="pci_user_read_config_byte",tag="d57be3affc84ce20"} 1
ebpf_exporter_ebpf_program_info{config="pci",id="280",program="pci_user_read_config_word",tag="d57be3affc84ce20"} 1
ebpf_exporter_ebpf_program_info{config="pci",id="281",program="pci_user_read_config_dword",tag="d57be3affc84ce20"} 1
ebpf_exporter_enabled_configs{name="pci"} 1
# HELP ebpf_exporter_pci_user_read_config_ops_total The number of operations reading pci configs
# TYPE ebpf_exporter_pci_user_read_config_ops_total counter
ebpf_exporter_pci_user_read_config_ops_total{pci_class="Bridge",pci_device="QEMU PCIe Host bridge",pci_subclass="Host bridge",pci_vendor="Red Hat, Inc."} 16
ebpf_exporter_pci_user_read_config_ops_total{pci_class="Mass storage controller",pci_device="QEMU NVM Express Controller",pci_subclass="Non-Volatile memory controller",pci_vendor="Red Hat, Inc."} 32
ebpf_exporter_pci_user_read_config_ops_total{pci_class="Unclassified device",pci_device="Virtio filesystem",pci_subclass="unknown pci subclass: 0x02 (class 0x00)",pci_vendor="Red Hat, Inc."} 32