Remove a stale comment about where trusted stack initialisation might go;
it actually went somewhere else.
As the CHERI permission mask is now wider, print permissions using 8 rather
than 4 hex digits in cheritest.
Adjust 'struct cheri_cap' used in kernel to use a 31-bit bitfield for
capability permissions rather than the previous 15-bit, now that we
have added user permissions.  Lose the previous padding out to a
32-bit word including 'unsealed' bit.
Tidy up kernel's CHERI register debugging code a bit; also ensure we print
permissions as 8- rather than 4-character wide.