uboot-phytec

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 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_XXX_load_image functions into superset functions,
  accepting additional arguments such as filenames, media load offset,
  and dedicated load addresses,
- Extend these functions 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 trampoline functions,
  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)
as well as SPI Flash and Y-Modem based UART loading.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>