piglit: upgrade to latest revision

Update piglit to latest git revision and update the branch name,
since the original one is no longer updated. Make sure the VK
tests are only enabled if VK is also enabled in PACKAGECONFIG,
and that this is opt-in, otherwise older systems fail to build.

Cherry picked from squashed commits:
  eb3a8d4c ("piglit: upgrade to latest revision")
  a27b06f7 ("piglit: upgrade to latest revision")
  bb091bc0 ("piglit: upgrade to latest revision")
  394746d1 ("piglit: upgrade to latest revision")
  5aec8cff ("piglit: upgrade to latest revision")
  fc4c8277 ("piglit: fix reproducibility")
  6fbec0f1 ("piglit: update to latest revision")
  8d23a0d4 ("piglit: upgrade to latest revision")
  5144d515 ("piglit: upgrade to latest revision")
  dd085bd5 ("piglit: upgrade to latest revision")
  9ba6df1b ("piglit: upgrade to latest revision")
  1ccd71eb ("piglit: upgrade to latest revision")

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Anuj Mittal <anuj.mittal@intel.com>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
Cc: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>