scripts/Makefile.lib: do not include CONFIG_DEVICE_TREE_INCLUDES in dtsi_include_list

scripts/Makefile.lib: do not include CONFIG_DEVICE_TREE_INCLUDES in dtsi_include_list

The commit mentioned in Fixes broke the
CONFIG_DEVICE_TREE_INCLUDES feature, with the result that any board
setting any non-empty value for that fails to build.

The parent of the mentioned commit refactoring a bit by introducing
the dtsi_include_list variable and changing cmd_dtc to loop over that
was fine.

However, the .dtsi files mentioned in CONFIG_DEVICE_TREE_INCLUDES are
not supposed to be generated via the build system. They are meant for
e.g. including a public key for verified boot (generated with the
key2dtsi script), or for injecting some stuff to the /config
node (say, a bootcmd or a load-environment setting or things like
that). The files can either live in-tree in a private branch or
completely outside, e.g. in some Yocto metadata.

But regardless, U-Boot's build system will never know anything about
them, so when the mentioned commit did

dtsi_include_list_deps = $(addprefix $(obj)/,$(subst $(quote),,$(dtsi_include_list)))

things broke, because if CONFIG_DEVICE_TREE_INCLUDES is for example
"/path/to/public_key.dtsi", this would add a dependency on
$(obj)//path/to/public_key.dtsi to each $(obj)/*.dtb target, yielding

make[3]: *** No rule to make target 'arch/arm/dts/imx6dl-aristainetos2c_7.dtb', needed by 'dtbs'.  Stop.

To fix that while preserving the introduced
CONFIG_EFI_CAPSULE_ESL_FILE behaviour, disentangle
CONFIG_DEVICE_TREE_INCLUDES from dtsi_include_list from which
dtsi_include_list_deps is built, and instead just add the items
directly to the $(foreach) loop.

Fixes: a958988b62 ("scripts/Makefile.lib: Add dtsi include files as deps for building DTB")
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Tested-by: Emil Kronborg <emil.kronborg@protonmail.com>