x86/asm/entry/64: Clean up and document various entry code details

x86/asm/entry/64: Clean up and document various entry code details

This patch does a lot of cleanup in comments and formatting,
but it does not change any code:

 - Rename 'save_paranoid' to 'paranoid_entry': this makes naming
   similar to its "non-paranoid" sibling, 'error_entry',
   and to its counterpart, 'paranoid_exit'.

 - Use the same CFI annotation atop 'paranoid_entry' and 'error_entry'.

 - Fix irregular indentation of assembler operands.

 - Add/fix comments on top of 'paranoid_entry' and 'error_entry'.

 - Remove stale comment about "oldrax".

 - Make comments about "no swapgs" flag in ebx more prominent.

 - Deindent wrongly indented top-level comment atop 'paranoid_exit'.

 - Indent wrongly deindented comment inside 'error_entry'.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/4640f9fcd5ea46eb299b1cd6d3f5da3167d2f78d.1424989793.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>