The previous version failed to build on alpha:
debian/virtio-modules-4.19.0-3-alpha-generic-di lib/modules/4.19.0-3-alpha-generic/kernel/drivers/i2c/i2c-core.ko
debian/i2c-modules-4.19.0-3-alpha-generic-di lib/modules/4.19.0-3-alpha-generic/kernel/drivers/i2c/i2c-core.ko
and sparc64:
debian/virtio-modules-4.19.0-3-sparc64-di lib/modules/4.19.0-3-sparc64/kernel/drivers/i2c/i2c-core.ko
debian/nic-modules-4.19.0-3-sparc64-di lib/modules/4.19.0-3-sparc64/kernel/drivers/i2c/i2c-core.ko
sparc64 was missing a i2c-modules package, but adding that just gets
it to the same state as alpha. On both architectures drm_kms_helper
is included in the virtio-modules package as a dependency of
virtio-gpu, and then i2c-core is included as a dependency of
drm_kms_helper.
I don't think it makes sense to make virtio-modules directly depend on
i2c-modules. (In fact I think virtio-modules was a mistake entirely.)
Instead, for all configurations that enable both DRM and virtio:
1. Add an fb-modules package if it doesn't already exist
2. Include drm and drm_kms_helper in it