kvm_sys: Update bindings.rs

Regenerate bindings.rs for kvm and add comments about how to generate it.
As a result, manually-added hack related to zero-sized arrays' alignment
was removed, as the bug had been fixed:
https://github.com/rust-lang/rust-bindgen/issues/684

BUG=none
TEST=build_test

Change-Id: I257975ce3cd4667b39381ddafd8b08d9e91de655
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2532546
Tested-by: Keiichi Watanabe <keiichiw@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Commit-Queue: Keiichi Watanabe <keiichiw@chromium.org>

hypervisor/src/kvm/mod.rs

@@ -1016,7 +1016,7 @@ impl From<&IrqRoute> for kvm_irq_routing_entry {
                         address_lo: *address as u32,
                         address_hi: (*address >> 32) as u32,
                         data: *data,
-                        pad: 0,
+                        ..Default::default()
                     },
                 },
                 ..Default::default()