firmware/shim: update linkfarm exclusions

firmware/shim: update linkfarm exclusions

Some intermediate files weren't considered at all at the time. Also
after its introduction, various changes to the build environment have
rendered the exclusion sets stale. For example, we now have some .*.cmd
files in the build tree. Combine all respective patterns into a single
.* one, seeing that we don't have any actual source files matching this
pattern in the tree. Add other patterns as well as individual files.
Also introduce LINK_EXCLUDE_PATHS to deal with entire directories full
of generated headers as well as a few specific files the names of which
are too generic to list under LINK_EXCLUDES.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>