Instead of avoiding CFI entirely on the TLB flush helpers, reorganize
the code so that the CFI machinery can deal with it. The important
things to take into account are:
- functions in asm called indirectly from C need to be defined using
  SYM_TYPED_FUNC_START()
- a reference to the asm function needs to be visible to the compiler,
  in order to get it to emit the typeid symbol.

The latter means that defining the cpu_tlb_fns structs is best done from
C code, so that the references in the static initializers will be
visible to the compiler.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>