efi_loader: Sporadic build failure: Error: file not found: <path>/capsule_esl_file

[Anthony Pighin (Nokia)]

Following the introduction of commit fd58c275f6ba524101ba0990e53f5a11ac390bd0,
we have seen sporadic build failures with the following footprint:

<path>/u-boot/2025.04/git/lib/efi_loader/efi_capsule_key.S:14: 
Error: file not found: <path>/u-boot/2025.04/git/capsule_esl_file

Upstream commit 739ad58dbee874a3ad3bddd116e995212a254e07 also touched this area,
and we pulled it back into our build as a test. However, it still appears there is a missing
dependency:

--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -87,7 +87,7 @@ $(objtree)/capsule_esl_file: FORCE
        fi
        $(call cmd,capsule_esl_gen)

-$(obj)/efi_capsule.o: $(objtree)/capsule_esl_file FORCE
+$(obj)/efi_capsule.o $(obj)/efi_capsule_key.o: $(srctree)/capsule_esl_file FORCE
 asflags-y += -DCAPSULE_ESL_PATH=\"$(objtree)/capsule_esl_file\"
 endif

Anthony