fuzz: Add fuzzing for core and i2c

Add fuzzing infrastructure and a fuzz target handling mctp-i2c packets.
After running for a few days with honggfuzz this achieves close to
complete line coverage of core.c

Change-Id: I6cd7361e6f600831a319f06fb7c7c0d2186fd7de
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
diff --git a/tests/meson.build b/tests/meson.build
index 96d7d6b..eb398b0 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -29,3 +29,5 @@
         ),
     )
 endforeach
+
+subdir('fuzz')