arm: remove interrupt nesting by ipi_preempt()/ipi_hardclock()

This was needed when intr_ipi_dispatch() was called by hardware-specific
IPI interrupt routines which didn't save the trap frame. Now all ARM
interrupts pass through INTRNG which will have already saved the trap
frame and disabled preemption.

Remove the conditional trapframe/argument passing to the handlers.

Reviewed by: andrew
Differential Revision: https://reviews.freebsd.org/D37938