sandbox: Use the reset driver to handle reset

Move sandbox over to use the reset uclass for reset, instead of a direct
call to do_reset(). This allows us to add tests.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 29e7b5b..907554f 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -46,3 +46,4 @@
 CONFIG_UT_DM=y
 CONFIG_UT_ENV=y
 CONFIG_CLK=y
+CONFIG_RESET=y