v4l2_codec2: Don't allow clang-format to merge include groups.

The clang-format configuration for the code under v4l2_codec2 seems to
be unable to distingush between std includes (e.g. "<string.h>") and
other includes (e.g. #include "<utils/Log.h>") and groups them
together. To avoid this this CL adds "IncludeBlocks: Preserve" to the
.clang-format file.

Bug: 143333813
Test: ./clang-format and checked output
Change-Id: I9f18daa783b089d7493f686797d474ad1c64f00a

.clang-format

@@ -31,3 +31,5 @@ IndentCaseLabels: false
 ReflowComments: false
 # Android does support C++11 now.
 Standard: Cpp11
+# Don't merge include blocks.
+IncludeBlocks: Preserve