Merge tag 'efi-2026-03-14' of https://source.denx.de/u-boot/custodians/u-boot-efi...

Pull request efi-2026-03-14

CI: https://source.denx.de/u-boot/custodians/u-boot-efi/-/pipelines/29512

UEFI:

* Require at least 128 KiB of stack space to use EFI sub-system.
* Avoid buffer overrun in efi_var_restore().
* Avoid superfluous variable store writes on unchanged data
* Implement SPI Flash store for EFI variables.
* Add an efidebug ecpt sub-command to display the ECPT table
  and a unit test for the command.

Others:

* Add missing include string.h to make exception command build again.
* lib: uuid: add EBBR 2.1 conformance profile GUID