The sensinode platform does not support .upload and .serialdump
Their presence in the makefile has confused in the past confused
some users. This commit removes them
The commit also removes the $(OBJECTDIR)/%.rel: %.cS recipe which
is not used by either 8051 platform and is probably broken anyway,
since it has been unmaintained for years
Historically $(OBJECTDIR) was created when Makefile.include is read. A
consequence is that combining "clean" with "all" (or any other build
target) results in an error because the clean removes the object
directory that is required to exist when building dependencies.
Creating $(OBJECTDIR) on-demand ensures it is present when needed.
Removed creation of $(OBJECTDIR) on initial read, and added an order-only
dependency forcing its creation all Makefile* rules where the target is
explicitly or implicitly in $(OBJECTDIR).
