object_footprint: don't adjust IDT size

The size of the interrupt descriptor table is not really
relevant to this test.

If any driver enabled for the target board gets enabled and
has a priority level outside the IDT range, gen_idt.py is properly
reporting an error. The old C-based gen_idt seems to have allowed
this to slide by.

Issue: ZEP-2496
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>