doc: Use proper note and warning annotations

The documentation contains plenty of notes and warnings. Enable
special rendering of these blocks by converting the note prefix
into a .. note:: annotation.

Change-Id: I34e26ca6bf313d335672ab6c2645741900338822
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/plat/rpi3.rst b/docs/plat/rpi3.rst
index d155fcb..38c3dfa 100644
--- a/docs/plat/rpi3.rst
+++ b/docs/plat/rpi3.rst
@@ -270,11 +270,12 @@
   BL32_EXTRA1=tee-pager_v2.bin  BL32_EXTRA2=tee-pageable_v2.bin``
   to put the binaries into the FIP.
 
-  Note: If OP-TEE is used it may be needed to add the following options to the
-  Linux command line so that the USB driver doesn't use FIQs:
-  ``dwc_otg.fiq_enable=0 dwc_otg.fiq_fsm_enable=0 dwc_otg.nak_holdoff=0``.
-  This will unfortunately reduce the performance of the USB driver. It is needed
-  when using Raspbian, for example.
+  .. warning::
+     If OP-TEE is used it may be needed to add the following options to the
+     Linux command line so that the USB driver doesn't use FIQs:
+     ``dwc_otg.fiq_enable=0 dwc_otg.fiq_fsm_enable=0 dwc_otg.nak_holdoff=0``.
+     This will unfortunately reduce the performance of the USB driver. It is
+     needed when using Raspbian, for example.
 
 - ``TRUSTED_BOARD_BOOT``: This port supports TBB. Set this option to 1 to enable
   it. In order to use TBB, you might want to set ``GENERATE_COT=1`` to let the