[profile] Allow interrupts to be excluded from profiling results

Interrupt processing adds noise to profiling results.  Allow
interrupts (from within protected mode) to be profiled separately,
with time spent within the interrupt handler being excluded from any
other profiling currently in progress.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/profile.c

@@ -40,6 +40,9 @@ FILE_LICENCE ( GPL2_OR_LATER );
  * to avoid the use of floating-point instructions.
  */
 
+/** Accumulated time excluded from profiling */
+unsigned long profile_excluded;
+
 /**
  * Format a hex fraction (for debugging)
  *