dm: core: Allow driver model to be disabled for TPL

Since TPL often needs to be very very small it may not make sense to
enable driver model. Add an option for this.

This changes brings the 'rock' board under the TPL limit with gcc 4.9.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/Makefile

@@ -2,7 +2,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-$(CONFIG_$(SPL_)DM)		+= core/
+obj-$(CONFIG_$(SPL_TPL_)DM)	+= core/
 obj-$(CONFIG_$(SPL_)CLK)	+= clk/
 obj-$(CONFIG_$(SPL_)LED)	+= led/
 obj-$(CONFIG_$(SPL_)PINCTRL)	+= pinctrl/

drivers/core/Kconfig

@@ -21,6 +21,20 @@ config SPL_DM
 	  and devices in SPL, so 1KB should be enable. See
 	  CONFIG_SYS_MALLOC_F_LEN for more details on how to enable it.
 
+config TPL_DM
+	bool "Enable Driver Model for TPL"
+	depends on DM && TPL
+	help
+	  Enable driver model in TPL. You will need to provide a
+	  suitable malloc() implementation. If you are not using the
+	  full malloc() enabled by CONFIG_SYS_SPL_MALLOC_START,
+	  consider using CONFIG_SYS_MALLOC_SIMPLE. In that case you
+	  must provide CONFIG_SYS_MALLOC_F_LEN to set the size.
+	  In most cases driver model will only allocate a few uclasses
+	  and devices in SPL, so 1KB should be enough. See
+	  CONFIG_SYS_MALLOC_F_LEN for more details on how to enable it.
+	  Disable this for very small implementations.
+
 config DM_WARN
 	bool "Enable warnings in driver model"
 	depends on DM