Kconfig: Move CONFIG_BOOTSTAGE to Kconfig

Move CONFIG_BOOT_STAGE and its associated options to Kconfig. Adjust
existing users and code.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 3731c71..288aacc 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -15,3 +15,5 @@
 CONFIG_DM_USB=y
 CONFIG_USB_EMUL=y
 CONFIG_USB_STORAGE=y
+CONFIG_BOOTSTAGE=y
+CONFIG_BOOTSTAGE_REPORT=y