spl: Make image loader infrastructure more universal

The current U-Boot SPL image loader infrastructure is very powerful,
able to initialize and load from a variety of boot media however it
is strongly geared towards loading specific types of images in a very
specific way. To address the need being able to use this infrastructure
to load arbitrary image files go ahead and refactor it as follows:

- Refactor existing spl_mmc_load_image function into superset function,
  accepting additional arguments such as filenames and media load offset
  (same concept can also be applied toother spl_XXX_load_image functions)
- Extend the loader function to "remember" their peripheral initialization
  status so that the init is only done once during the boot process,
- Extend the FIT image loading function to allow skipping the parsing/
  processing of the FIT contents (so that this can be done separately
  in a more customized fashion)
- Populate the SPL_LOAD_IMAGE_METHOD() list with a trampoline function,
  invoking the newly refactored superset functions in a way to maintain
  compatibility with the existing behavior

This refactoring initially covers MMC/SD card loading (RAW and FS-based).

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

include/spl.h

@@ -108,6 +108,15 @@ struct spl_load_info {
  */
 binman_sym_extern(ulong, u_boot_any, image_pos);
 
+/**
+ * spl_load_simple_fit_skip_processing() - Hook to allow skipping the FIT
+ *	image processing during spl_load_simple_fit().
+ *
+ * Return true to skip FIT processing, false to preserve the full code flow
+ * of spl_load_simple_fit().
+ */
+bool spl_load_simple_fit_skip_processing(void);
+
 /**
  * spl_load_simple_fit() - Loads a fit image from a device.
  * @spl_image:	Image description to set up
@@ -330,6 +339,23 @@ int spl_dfu_cmd(int usbctrl, char *dfu_alt_info, char *interface, char *devstr);
 int spl_mmc_load_image(struct spl_image_info *spl_image,
 		       struct spl_boot_device *bootdev);
 
+/**
+ * spl_mmc_load() - Load an image file from MMC/SD media
+ *
+ * @param spl_image	Image data filled in by loading process
+ * @param bootdev	Describes which device to load from
+ * @param filename	Name of file to load (in FS mode)
+ * @param raw_part	Partition to load from (in RAW mode)
+ * @param raw_sect	Sector to load from (in RAW mode)
+ *
+ * @return 0 on success, otherwise error code
+ */
+int spl_mmc_load(struct spl_image_info *spl_image,
+		 struct spl_boot_device *bootdev,
+		 const char *filename,
+		 int raw_part,
+		 unsigned long raw_sect);
+
 /**
  * spl_invoke_atf - boot using an ARM trusted firmware image
  */