mesa: Implement GL_FRAMEBUFFER_ATTACHMENT_LAYERED query.

From section 6.1.18 (Renderbuffer Object Queries) of the GL 3.2 spec,
under the heading "If the value of FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE
is TEXTURE, then":

    If pname is FRAMEBUFFER_ATTACHMENT_LAYERED, then params will
    contain TRUE if an entire level of a three-dimesional texture,
    cube map texture, or one-or two-dimensional array texture is
    attached. Otherwise, params will contain FALSE.

Fixes piglit tests:
- spec/!OpenGL 3.2/layered-rendering/framebuffer-layered-attachments
- spec/!OpenGL 3.2/layered-rendering/framebuffertexture-defaults

Cc: "10.0" <mesa-stable@lists.freedesktop.org>

Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>

v2: Don't include "EXT" in the error message, since this query only
makes sensen in context versions that have adopted
glGetFramebufferAttachmentParameteriv().

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/mesa/main/fbobject.c

@@ -2964,6 +2964,18 @@ _mesa_GetFramebufferAttachmentParameteriv(GLenum target, GLenum attachment,
                        " invalid FBO attachment structure");
       }
       return;
+   case GL_FRAMEBUFFER_ATTACHMENT_LAYERED:
+      if (!_mesa_has_geometry_shaders(ctx)) {
+         goto invalid_pname_enum;
+      } else if (att->Type == GL_TEXTURE) {
+         *params = att->Layered;
+      } else if (att->Type == GL_NONE) {
+         _mesa_error(ctx, err,
+                     "glGetFramebufferAttachmentParameteriv(pname)");
+      } else {
+         goto invalid_pname_enum;
+      }
+      return;
    default:
       goto invalid_pname_enum;
    }