aarch64: do not accept 0 as a valid address size
aarch64: do not accept 0 as a valid address size

The newly-added KVM_CHECK_EXTENSION call to retrieve
KVM_CAP_ARM_VM_IPA_SIZE was checking for errors by looking for return
values less than 0, but KVM_CHECK_EXTENSION returns 0 for unknown
extensions (e.g. on older kernels before this extension was introduced).

Treat 0 as unsupported as well so the default 40-bit size is returned in
this case.

BUG=b:215174283
BUG=b:210727578
TEST=Boot crosvm on kevin (arm device with 4.4 host kernel)

Fixes: 891ea3e88aa3 ("aarch64: limit high MMIO addresses to VM phys addr range")
Change-Id: I19a3ae00862882c030c1e776cb3ca10edeffd339
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3399344
Reviewed-by: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm