irq: introduce 'direct' interrupt API definition

These interrupts are for ISRs that need the lowest possible latency.
They do not take parameters and are installed directly in the interrupt
vector table.

Issue: ZEP-1038
Change-Id: I7583e9191dd32d9253ad933181d2103a6e191dea
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>