ANDROID: KVM: arm64: Add documentation for range-based guest HVCs

A new flag (KVM_FUNC_HAS_RANGE) advertises the availability of ranges
for mmio-guard and memory sharing. It is recommended to use these new
HVCs whenever a region bigger than the granule size needs to be
processed. Document them.

Bug: 278749606
Bug: 243642516
Change-Id: I1dc9e9c3ce983f35566470260ca7266cf2c54cf3
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>