dm: core: Add Kconfig for simple bus driver

Add Kconfig entries for the simple-bus driver, both for U-Boot
and for SPL. The simple-bus is enabled by default in U-Boot and
disabled by default in SPL to preserve the original behavior.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>
Modified to fit on top of Masahiro's $(SPL) setup:
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/Kconfig b/drivers/core/Kconfig
index 788f8b7..41f4e69 100644
--- a/drivers/core/Kconfig
+++ b/drivers/core/Kconfig
@@ -105,4 +105,19 @@
 
 	  If you are unsure about this, Say N here.
 
+config SIMPLE_BUS
+	bool "Support simple-bus driver"
+	depends on DM && OF_CONTROL
+	default y
+	help
+	  Supports the 'simple-bus' driver, which is used on some systems.
+
+config SPL_SIMPLE_BUS
+	bool "Support simple-bus driver in SPL"
+	depends on SPL_DM && SPL_OF_CONTROL
+	default n
+	help
+	  Supports the 'simple-bus' driver, which is used on some systems
+	  in SPL.
+
 endmenu