Merge branch '2023-10-17-spl-test-some-load-methods'

To quote the author:
This series adds some tests for various SPL load methods, with the
intent of helping debug v6 of [1]. With that in mind, notable omissions
include NAND and ROMAPI, which both lack sandbox implementations, and
OS_BOOT, which I have deferred due to its complexity. Semihosting is
also omitted, but I think we can test that with qemu.

In order to test all of these methods, we must first generate suitable
images, possibly on filesystems. While other tests have historically
generated these images using external tools (e.g. mkimage, mkfs, etc.),
I have chosen to generate them on the fly. This is for a few reasons:

- By removing external dependencies on pytest to create certain files,
  the tests become self-contained. This makes them easier to iterate on
  and debug.
- By generating tests at runtime, we can dynamically vary the content.
  This helps detect test failures, as even if tests are loaded to the
  same location, the expected content will be different.
- We are not testing the image parsers themselves (e.g.
  spl_load_simple_fit or fs_read) but rather the load methods (e.g.
  spl_mmc_load_image). It is unnecessary to exercise full functionality
  or generate 100% correct images.
- By reducing functionality to only what is necessary, the complexity of
  various formats can often be greatly reduced.

This series depends on [2-3], which are small fixes identified through
this patch set. The organization of patches in this series is as
follows:

- General fixes for bugs which are unlikely to be triggered outside of
  this series
- Changes to IMX8 container images to facilitate testing
- General prep. work, particularly regarding linker issues
- The tests themselves

Passing CI at [4].

[1] https://lore.kernel.org/all/20230731224304.111081-1-sean.anderson@seco.com/
[2] https://lore.kernel.org/all/20230930204246.515254-1-seanga2@gmail.com/
[3] https://lore.kernel.org/all/20231008014748.1987840-1-seanga2@gmail.com/
[4] https://source.denx.de/u-boot/custodians/u-boot-clk/-/pipelines/18128