x86/entry: Cleanup idtentry_enter/exit

Remove the temporary defines and fixup all references.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200722220520.855839271@linutronix.de