scons: Pull bytesToCppArray into build_tools.

This mechanism will be used by various small scripts which perform steps
of the build.

Change-Id: I91d842c022d6f568715e8a10310894cb8afbab20
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49398
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Maintainer: Gabe Black <gabe.black@gmail.com>

src/SConscript

@@ -54,7 +54,7 @@ import SCons
 
 from gem5_scons import Transform, warning, error, ToValue, FromValue
 from gem5_scons.sources import *
-from gem5_scons.util import bytesToCppArray
+from blob import bytesToCppArray
 
 Export(SourceFilter.factories)