ANDROID: GKI: enable options to run GKI as Microdroid guest

Starting with android15-6.6 we are planning to support running GKI as
Microdroid guest kernel to enable VM use cases that require loading
vendor-provided kernel modules into guest VM (e.g. device assignment).

Additionally adjust the rockpi4_gki.fragment to address the build
breakage caused by changes to the gki_defconfig.

Bug: 302467077
Test: see 613f7c1b2fef7ebe3edd1f89279cb40d2a7bf8fb
Change-Id: Ide66b713a0edee869264ee9dd1def5f21d28c862
Signed-off-by: Nikita Ioffe <ioffe@google.com>