treewide: Rename "unencrypted" to "decrypted"

Back then when the whole SME machinery started getting mainlined, it
was agreed that for simplicity, clarity and sanity's sake, the terms
denoting encrypted and not-encrypted memory should be "encrypted" and
"decrypted". And the majority of the code sticks to that convention
except those two. So rename them.

The intent of "encrypted" and "decrypted" is to represent the binary
concept of memory which is encrypted and of memory which is not.

The further differentiation between decrypted and unencrypted memory is
not needed in the code (for now) and therefore keep things simple by
using solely the two terms.

No functional changes.

[ Convert forgotten s390 and ppc function variants. ]
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
10 files changed