xen: enforce __init in common/device-tree/*-build.c

Code in domain-build.c and dom0less-build.c was migrated from init-only
files. Thus, they contain only __init functions. Enforce this at build
time.

Fixes: ad03faa942 ("xen/common: dom0less: make some parts of Arm's CONFIG_DOM0LESS common")
Fixes: d07b7369aa ("xen/common: dom0less: introduce common domain-build.c")
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/common/device-tree/Makefile

@@ -1,8 +1,8 @@
 obj-y += bootfdt.init.o
 obj-y += bootinfo.init.o
 obj-y += device-tree.o
-obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += domain-build.o
-obj-$(CONFIG_DOM0LESS_BOOT) += dom0less-build.o
+obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += domain-build.init.o
+obj-$(CONFIG_DOM0LESS_BOOT) += dom0less-build.init.o
 obj-$(CONFIG_OVERLAY_DTB) += dt-overlay.o
 obj-y += intc.o
 obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += kernel.o