Checkpatch: Update rules

Added a few rules to suppress non relevant warnings and add an error
message whenever C99 comments are used.

Signed-off-by: Salome Thirot <salome.thirot@arm.com>
Change-Id: I58e3d78c03cd8366ceb766c8fb81dd564c2a5094
diff --git a/checkpatch/checkpatch.conf b/checkpatch/checkpatch.conf
index 0a20b50..436cd2f 100644
--- a/checkpatch/checkpatch.conf
+++ b/checkpatch/checkpatch.conf
@@ -1,5 +1,5 @@
 #-------------------------------------------------------------------------------
-# Copyright (c) 2018-2019, Arm Limited and Contributors. All rights reserved.
+# Copyright (c) 2018-2021, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -18,4 +18,7 @@
 --ignore CONST_STRUCT
 --ignore INITIALISED_STATIC
 --ignore SPDX_LICENSE_TAG
+--ignore C99_COMMENT_TOLERANCE
+--ignore ARRAY_SIZE
+--ignore QUOTED_WHITESPACE_BEFORE_NEWLINE
 --show-types