Mark both the function prototype and definition as noreturn in order to
prevent the compiler from doing transformations which confuse objtool
like so:

  vmlinux.o: warning: objtool: sme_enable+0x71: unreachable instruction

This triggers with gcc-12.

Add it and sev_es_terminate() to the objtool noreturn tracking array
too. Sort it while at it.
Suggested-by: Michael Matz <matz@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220824152420.20547-1-bp@alien8.de