Revert "x86/ftrace: Use alternative RET encoding"

This reverts commit 3eb602ad.

Revert the backport of upstream commit

  1f001e9d ("x86/ftrace: Use alternative RET encoding")

in favor of a proper backport after backporting the commit which adds
__text_gen_insn().

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>