Cleanup X86 IOAPIC code from interrupt remapping details

These patches move all interrupt remapping specific checks out of the
x86 core code and replaces the respective call-sites with function
pointers. As a result the interrupt remapping code is better abstraced
from x86 core interrupt handling code.

The code was rebased to v3.8-rc4 and tested on systems with AMD-Vi and
Intel VT-d (both capable of interrupt remapping). The systems were
tested with IOMMU enabled and with IOMMU disabled. No issues were found.
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