util: Add piglit_split_string_to_array()

This splits a string into an array of strings, which is useful for
splitting the string returned by eglQueryString(EGL_EXTENSIONS).

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
util: Move piglit_strip_arg()

Move it from piglit-framework-gl.h to piglit-util.h. This is a generic
utility that should not be restricted GL tests.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
egl_ext_client_extensions: Add initial tests

Add tests for the conformance tests listed in the
EGL_EXT_client_extensions spec.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>