docs-rst: add input docs at main index and use kernel-figure

The input subsystem documentation got converted into ReST.

Add it to the main documentation index and use kernel-figure
for the two svg images there.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/index.rst

@@ -67,6 +67,7 @@ needed).
    driver-api/index
    core-api/index
    media/index
+   input/index
    gpu/index
    security/index
    sound/index

Documentation/input/ff.rst

@@ -130,11 +130,11 @@ See <uapi/linux/input.h> for a description of the ff_effect struct.  You
 should also find help in a few sketches, contained in files shape.svg
 and interactive.svg:
 
-.. figure:: shape.svg
+.. kernel-figure:: shape.svg
 
     Shape
 
-.. figure:: interactive.svg
+.. kernel-figure:: interactive.svg
 
     Interactive