xen/dt: Rename bootfdt.c -> bootinfo-fdt.c

bootinfo-fdt.c will eventually contain bootfdt helpers that make heavy
use of bootinfo. To simplify git history do the rename here explicitly.
A later patch extracts bootinfo-independent helpers into bootfdt.c.

Doing so here would needlessly pollute the diffs.

Not a functional change.

Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@amd.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>

xen/common/device-tree/Makefile

@@ -1,4 +1,4 @@
-obj-y += bootfdt.init.o
+obj-y += bootinfo-fdt.init.o
 obj-y += bootinfo.init.o
 obj-y += device-tree.o
 obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += domain-build.init.o