x86/entry: Cleanup idtentry_entry/exit_user

Cleanup the temporary defines and use irqentry_ instead of idtentry_.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200722220520.602603691@linutronix.de