common: convert compulab splash load code to common code

Move board/compulab/common/splash.c code to
common/splash_source.c to make it available for everybody. This move
renames cl_splash_screen_prepare() to splash_source_load(), and
the compilation of this code is conditional on CONFIG_SPLASH_SOURCE.

splash_source features:
* Provide a standardized way for declaring board specific splash screen
  locations
* Provide existing routines for auto loading the splash image from the
  locations as declared by the board
* Introduce the "splashsource" environment variable, which makes it
  possible to select the splash image source.

cm-t35 and cm-fx6 are updated to use the modified version.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Anatolij Gustschin <agust@denx.de>
Reviewed-by: Tom Rini <trini@ti.com>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
diff --git a/include/configs/cm_fx6.h b/include/configs/cm_fx6.h
index b92ba97..1f64495 100644
--- a/include/configs/cm_fx6.h
+++ b/include/configs/cm_fx6.h
@@ -313,6 +313,7 @@
 #define CONFIG_VIDEO_SW_CURSOR
 
 #define CONFIG_SPLASH_SCREEN
+#define CONFIG_SPLASH_SOURCE
 #define CONFIG_CMD_BMP
 #define CONFIG_VIDEO_BMP_RLE8
 
diff --git a/include/configs/cm_t35.h b/include/configs/cm_t35.h
index 9767512..b2a9f35 100644
--- a/include/configs/cm_t35.h
+++ b/include/configs/cm_t35.h
@@ -310,6 +310,7 @@
 
 #define CONFIG_LCD
 #define CONFIG_SPLASH_SCREEN
+#define CONFIG_SPLASH_SOURCE
 #define CONFIG_CMD_BMP
 #define CONFIG_BMP_16BPP
 #define CONFIG_SCF0403_LCD
diff --git a/include/splash.h b/include/splash.h
index 89ee7b2..a60e895 100644
--- a/include/splash.h
+++ b/include/splash.h
@@ -22,7 +22,18 @@
 #ifndef _SPLASH_H_
 #define _SPLASH_H_
 
+enum splash_storage {
+	SPLASH_STORAGE_NAND,
+	SPLASH_STORAGE_SF,
+};
+
+struct splash_location {
+	char *name;
+	enum splash_storage storage;
+	u32 offset;	/* offset from start of storage */
+};
 
+int splash_source_load(struct splash_location *locations, uint size);
 int splash_screen_prepare(void);
 
 #ifdef CONFIG_SPLASH_SCREEN_ALIGN