lib: move prefault helpers to igt_debugfs.c

This way all debugfs library code is in one place, ready for some api
documentation care.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

lib/drmtest.c

@@ -425,44 +425,6 @@ void igt_cleanup_aperture_trashers(void)
 	free(trash_bos);
 }
 
-#define PREFAULT_DEBUGFS "/sys/module/i915/parameters/prefault_disable"
-static void igt_prefault_control(bool enable)
-{
-	const char *name = PREFAULT_DEBUGFS;
-	int fd;
-	char buf[2] = {'Y', 'N'};
-	int index;
-
-	fd = open(name, O_RDWR);
-	igt_require(fd >= 0);
-
-	if (enable)
-		index = 1;
-	else
-		index = 0;
-
-	igt_require(write(fd, &buf[index], 1) == 1);
-
-	close(fd);
-}
-
-static void enable_prefault_at_exit(int sig)
-{
-	igt_enable_prefault();
-}
-
-void igt_disable_prefault(void)
-{
-	igt_prefault_control(false);
-
-	igt_install_exit_handler(enable_prefault_at_exit);
-}
-
-void igt_enable_prefault(void)
-{
-	igt_prefault_control(true);
-}
-
 void igt_system_suspend_autoresume(void)
 {
 	int ret;