doc: spm: update messaging method field

As per FF-A v1.0 spec, Table 3.1, messaging method field also contains
information about whether partition supports managed exit or not.
Since a partition can support managed exit only if it supports direct
messaging, so there are two new possible values, managed exit with only
direct messaging or with both messaging methods.

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: Ic77cfb37d70975c3a36c56f8b7348d385735f378

docs/components/psa-ffa-manifest-binding.rst

@@ -112,6 +112,8 @@ Partition Properties
       - 0x0: direct messaging method
       - 0x1: indirect messaging method
       - 0x2: both direct and indirect messaging methods
+      - 0x3: direct messaging method with managed exit support
+      - 0x4: both messaging methods with managed exit support
 
 - has-primary-scheduler
    - value type: <empty>
@@ -244,4 +246,4 @@ Device Regions
 
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-*Copyright (c) 2019-2020, Arm Limited and Contributors. All rights reserved.*
+*Copyright (c) 2019-2021, Arm Limited and Contributors. All rights reserved.*