generic: Create generic board infrastructure and move misc.h to it

Instead of creating a misc.h file in each board directory, create a
generic board directory and declare misc.h there.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/generic/alloc.c

@@ -0,0 +1,13 @@
+// Dummy implementation for alloc commands
+//
+// Copyright (C) 2016  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "misc.h"
+
+// Return the maximum allocation size that can succeed up to 'reqsize'
+size_t alloc_maxsize(size_t reqsize)
+{
+    return reqsize;
+}