libtcgtpm cleanup after recent merge

Hi all,
we just merged https://github.com/coconut-svsm/svsm/pull/853 that
should move all the build objects of libtcgtpm (TPM, openssl, libcrt)
out-of-tree, using properly the Cargo OUT_DIR in the Makefile to put
all generated files under target/

As Jon reported in the PR, there could be some leftover and the build
can fail (see https://github.com/coconut-svsm/svsm/pull/853#issuecomment-3518566049)
so I suggest doing a distclean in libtcgtpm:

make -C libtcgtpm distclean

Or cleaning everything to be sure to have a clean environment doing:

git clean -xfd
git submodule foreach --recursive git clean -xfd

Note: this will remove all untracked files, so be careful if you have
something untracked there.

Thanks,
Stefano