drm/selftests: Rename the Kconfig option to CONFIG_DRM_DEBUG_SELFTEST

We want to add more DRM selftests, and there's not much point in
having a Kconfig option for every single one of them, so make
a generic one.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180503112217.37292-5-maarten.lankhorst@linux.intel.com
[mlankhorst: Fix i915/Kconfig.debug (ickle)]
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/Kconfig.debug

@@ -25,7 +25,7 @@ config DRM_I915_DEBUG
         select X86_MSR # used by igt/pm_rpm
         select DRM_VGEM # used by igt/prime_vgem (dmabuf interop checks)
         select DRM_DEBUG_MM if DRM=y
-	select DRM_DEBUG_MM_SELFTEST
+	select DRM_DEBUG_SELFTEST
 	select SW_SYNC # signaling validation framework (igt/syncobj*)
 	select DRM_I915_SW_FENCE_DEBUG_OBJECTS
 	select DRM_I915_SELFTEST