selftests: add tests for the HID-bpf initial implementation

The tests are pretty basic:
- create a virtual uhid device that no userspace will like (to not mess
  up the running system)
- attach a BPF prog to it
- open the matching hidraw node
- inject one event and check:
  * that the BPF program can do something on the event stream
  * can modify the event stream
- add another test where we attach/detach BPF programs to see if we get
  errors

Note: the Makefile is extracted from selftests/bpf so we can rebuild
the libbpf and bpftool components from the current kernel tree without
relying on system installed components.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

tools/testing/selftests/hid/config

@@ -0,0 +1,20 @@
+CONFIG_BPF_EVENTS=y
+CONFIG_BPFILTER=y
+CONFIG_BPF_JIT_ALWAYS_ON=y
+CONFIG_BPF_JIT=y
+CONFIG_BPF_KPROBE_OVERRIDE=y
+CONFIG_BPF_LSM=y
+CONFIG_BPF_PRELOAD_UMD=y
+CONFIG_BPF_PRELOAD=y
+CONFIG_BPF_STREAM_PARSER=y
+CONFIG_BPF_SYSCALL=y
+CONFIG_BPF=y
+CONFIG_CGROUP_BPF=y
+CONFIG_DEBUG_INFO_BTF=y
+CONFIG_FPROBE=y
+CONFIG_FTRACE_SYSCALLS=y
+CONFIG_FUNCTION_TRACER=y
+CONFIG_HIDRAW=y
+CONFIG_HID=y
+CONFIG_INPUT_EVDEV=y
+CONFIG_UHID=y