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/components/exception-handling.rst b/docs/components/exception-handling.rst
index 30600f9..8f74eb6 100644
--- a/docs/components/exception-handling.rst
+++ b/docs/components/exception-handling.rst
@@ -193,7 +193,7 @@
    6 and 5), the platform can partition into 4 secure priority ranges: ``0x0``,
    ``0x20``, ``0x40``, and ``0x60``. See `Interrupt handling example`_.
 
-Note:
+.. note::
 
    The Arm GIC architecture requires that a GIC implementation that supports two
    security states must implement at least 32 priority levels; i.e., at least 5
@@ -215,7 +215,7 @@
 ``ehf_pri_desc_t``, and declares a priority level, and shall be populated by the
 ``EHF_PRI_DESC()`` macro.
 
-Note:
+.. warning::
 
    The macro ``EHF_PRI_DESC()`` installs the descriptors in the array at a
    computed index, and not necessarily where the macro is placed in the array.