Silicon/SynQuacer/DeviceTree: increase GICV region to 64 KB

The KVM/ARM code requires that the GICV region is a multiple of the
page size, and refuses to enable v2-on-v3 support if this is not the
case, preventing us from running GICv2 VMs when the host runs with
64 KB pages.

The Cortex-A53 TRM describes the remaining part of the 64 KB window as
reserved, so we can safely describe it as having a size of 64 KB.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>