Platform: Add mps3/fvp_sse300 target

Add support for Corstone-300 Ethos-U55 FVP as mps3/fvp_sse300 platform

Change-Id: I41a3fd07665a0bc16be5a251b3789dfbadfe7e45
Signed-off-by: Marton Berke <marton.berke@arm.com>
diff --git a/docs/getting_started/tfm_secure_boot.rst b/docs/getting_started/tfm_secure_boot.rst
index 0e92f38..05fdb35 100644
--- a/docs/getting_started/tfm_secure_boot.rst
+++ b/docs/getting_started/tfm_secure_boot.rst
@@ -236,6 +236,8 @@
 +---------------------+-----------------+---------------+----------+----------------+--------------+
 | FVP_SSE300_MPS2     | No              | Yes           | Yes      | Yes            | No           |
 +---------------------+-----------------+---------------+----------+----------------+--------------+
+| FVP_SSE300_MPS3     | No              | Yes           | Yes      | Yes            | No           |
++---------------------+-----------------+---------------+----------+----------------+--------------+
 | LPC55S69            | Yes             | Yes           | No       | Yes            | No           |
 +---------------------+-----------------+---------------+----------+----------------+--------------+
 | Musca-A             | No              | No            | No       | No             | Yes          |