drm/doc: Update IGT documentation

The IGT documentation in this page is telling us to build it using
make. According to commit 67993c1 ("automake: Point builders at
meson") from the IGT project, this is deprecated and IGT should be
built with meson. Instead of having a documentation for IGT in this
page, point to their GitLab README, which should always be up to
date.
Signed-off-by: Leandro Ribeiro <leandrohr@riseup.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191030011211.47942-1-leandrohr@riseup.net

Documentation/gpu/drm-uapi.rst

@@ -254,36 +254,8 @@ Validating changes with IGT
 There's a collection of tests that aims to cover the whole functionality of
 DRM drivers and that can be used to check that changes to DRM drivers or the
 core don't regress existing functionality. This test suite is called IGT and
-its code can be found in https://cgit.freedesktop.org/drm/igt-gpu-tools/.
-
-To build IGT, start by installing its build dependencies. In Debian-based
-systems::
-
-	# apt-get build-dep intel-gpu-tools
-
-And in Fedora-based systems::
-
-	# dnf builddep intel-gpu-tools
-
-Then clone the repository::
-
-	$ git clone git://anongit.freedesktop.org/drm/igt-gpu-tools
-
-Configure the build system and start the build::
-
-	$ cd igt-gpu-tools && ./autogen.sh && make -j6
-
-Download the piglit dependency::
-
-	$ ./scripts/run-tests.sh -d
-
-And run the tests::
-
-	$ ./scripts/run-tests.sh -t kms -t core -s
-
-run-tests.sh is a wrapper around piglit that will execute the tests matching
-the -t options. A report in HTML format will be available in
-./results/html/index.html. Results can be compared with piglit.
+its code and instructions to build and run can be found in
+https://gitlab.freedesktop.org/drm/igt-gpu-tools/.
 
 Display CRC Support
 -------------------