Move the header file out of pw_boot_armv7m to serve as a public API
for the facade, making pw_boot_armv7m the implementation.
This allows targets to provide an alternate implementation of
pw_boot_Entry.
This is not possible today due to the implementation dependency in
pw_malloc_freelist which, with this change, is moved to the facade
instead.
Update includes in existing targets to use the new path and dependency,
they were already setting pw_boot_BACKEND.
Change-Id: I88f921df0efea58536349e04fe09d1b580a7e733
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/54022
Pigweed-Auto-Submit: Scott James Remnant <keybuk@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Scott James Remnant <keybuk@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
