tests/kms_flip: Skip VBlank tests in modules without VBlank

The kms_flip test relies on VBlank support, and this situation may
exclude some virtual drivers to take advantage of this set of tests.
This commit adds a mechanism that checks if a module has VBlank. If the
target module has VBlank support, kms_flip will run all the VBlank
tests; otherwise, the VBlank tests will be skipped. Additionally, this
commit improves the test coverage by checks if the function
drmWaitVBlank() returns EOPNOTSUPP (i.e., no VBlank support).

V7: Skip seq number checking and busy flip if the device doesn't support
vblank

V6: Set errno to zero before call drmWaitVBlank() (Chris Wilson)

V5: Drop the DRM_VBLANK_NEXTONMISS (Chris Wilson)

V4: Replace DRM_VBLANK_ABSOLUTE by DRM_VBLANK_RELATIVE and
DRM_VBLANK_NEXTONMISS

V3: Add documentation (Daniel Vetter)

V2: Add new branch coverage to check if VBlank is enabled or not and
update commit message

V1: Chris Wilson
  - Change function name from igt_there_is_vblank to kms_has_vblank
  - Move vblank function check from igt_aux to igt_kms
  - Utilizes memset in dummy_vbl variable
  - Directly return the result of drmWaitVBlank()

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>