pc-bios/s390-ccw: Merge netboot.mak into the main Makefile

Now that the netboot code has been merged into the main s390-ccw.img,
it also does not make sense to keep the build rules in a separate
file. Thus let's merge netboot.mak into the main Makefile.

Message-Id: <20240621082422.136217-7-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
2 files changed