ANDROID: Add initial rockpi4_defconfig

This is for the Rock Pi 4B board from Radxa with Rockchip's RK3399.

Bug: 118442619
Change-Id: If2ba4198ef268e5b249e909b1987d52f1c8d0def
Signed-off-by: Tristan Muntsinger <muntsinger@google.com>
Co-developed-by: Alistair Delva <adelva@google.com>
Signed-off-by: Alistair Delva <adelva@google.com>
[maennich: Folded the following patch into this one
           7388b79c ("ANDROID: Catch rockpi4_defconfig up with gki_defconfig")]
Signed-off-by: Matthias Maennich <maennich@google.com>