This insures the common exception handler will not be
   re-entered. The handler does not support nested interrupts
   and the interrupt stack pointer and context will be overwritten
   resulting in hard to debug hardfaults.

   If all the priorities are equal the NVIC prevents the
   preemption. The startup code defaults all the priorities
   to the same value 128.

   This change safeguards in 2 ways 1) By disabling
   CONFIG_ ARCH_IRQPRIO: up_prioritize_irq cannot be called.
   This will insure that all HW interrupts are at the same
   priority.

   2) By disabling CONFIG_ARCH_HIPRI_INTERRUP, the common
   exception will disable any interrupts during interrupt
   processing.