This was done by code inspection; I have no way to test this. I also had a hard time finding documentation on the GIC register map, but the `GICD_*` definitions in `gic_v3_reg.h` suggest this size is correct.
Hopefully @whu or @kevans can report on if it fixes the observed boot-time panic.
-----
Distilled from the PR, the following output shows the overlap:
```
gic0: <ARM Generic Interrupt Controller v3.0> iomem 0xffff0000-0x10000ffff, ...... on acpi0
...
ram0: reserving memory region: 100000000-fc0000000
panic: ram_attach: resource 7 failed to attach
```