sandbox: select CONFIG_64BIT for sandbox

Select CONFIG_64BIT so that we pass the -m64 option (instead of -m32) to
static analysis tools.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>

arch/sandbox/Kconfig

@@ -46,6 +46,7 @@ config HOST_32BIT
 
 config HOST_64BIT
 	def_bool $(cc-define,_LP64)
+	select 64BIT
 
 config HOST_HAS_SDL
 	def_bool $(success,sdl2-config --version)