ANDROID: make virtio drivers needed for Microdroid built-in

Virtio drivers for Microdroid are now built in the kernel. This is to
unburden the GKI process; Microdroid kernel doesn't need to be updated
when the GKI prebuilts are updated. Before this change, Microdroid
kernel used the modules built for GKI. This in turn meant that
Microdroid kernel has to be updated everytime the GKI (and its modules)
are updated - because KMI is not stable until it gets frozen. By making
the drivers built-in, Microdroid doesn't need to modules from GKI and
can be completely decoupled from the GKI process.

Bug: 231117670
Test: run microdroid with this kernel
Signed-off-by: Jiyong Park <jiyong@google.com>
Change-Id: I337f27457f62032c80c3a6d36fe8ef9cf90294f7