piglit: Add missing glslang dependencies

The vulkan configuration requires glslangValidator for build and
runtime.

Fixes configure error:
```
| CMake Error at CMakeLists.txt:191 (message):
|   glslangValidator required by vulkan tests not found
```

Fixes runtime error:
```
name: vulkan@shaders@fs-large-local-array
    result: fail
    returncode: 1
    out:
    err: glslangValidator: No such file or directory
glslangValidator failed
```

Signed-off-by: Tom Hochstein <tom.hochstein@nxp.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
(cherry picked from commit 89423cc3)
Signed-off-by: Steve Sakoman <steve@sakoman.com>