arch/x86: Expose function do get DRHDs from DMAR ACPI table

This is part of Intel VT-D and how to discover capabilities, base
addresses and so on in order to start taking advantage from it.

There is a lot to get from there, but currently we are interested only
by getting the remapping hardware base address. And more specifically
for interrupt remapping usage.

There might be more than one of such hardware so the exposed function is
made to retrieve all of them.

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>