xen/arm: Instruction prefetch abort (X) mem_event handling

Add missing structure definition for iabt and use the LPAE XN bit to set eXecute mem_event traps.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
tools/tests: Enable xen-access on ARM

On ARM the guest memory doesn't start from 0, thus we include the required headers and define GUEST_RAM_BASE_PFN in both architecture to be passed to mem_access as the starting address. We also define the ARM specific test_and_set_bit function.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>