selftests: hid: tests: test_wacom_generic: add tests for display devices and opaque...

selftests: hid: tests: test_wacom_generic: add tests for display devices and opaque devices

Verify Wacom devices set INPUT_PROP_DIRECT on display devices and
INPUT_PROP_POINTER on opaque devices. Verify INPUT_PROP_POINTER
is not set on display devices and INPUT_PROP_DIRECT is not set
on opaque devices.

Moved test_prop_pointer into TestOpaqueTablet. Created a
DirectTabletTest mixin class for test_prop_direct that can be
inherited by display tablet test classes.Used DirectTabletTest
for TestDTH2452Tablet case.

Signed-off-by: Alex Tran <alex.t.tran@gmail.com>
Tested-by: Erin Skomra <erin.skomra@wacom.com>
Reviewed-by: Erin Skomra <erin.skomra@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>