ANDROID: drm/virtgpu api: create context init feature

This change allows creating contexts of different types, determined
by an associated capset ID.  For example, the current capsets:

VIRTIO_GPU_CAPSET_VIRGL
VIRTIO_GPU_CAPSET_VIRGL2

define a Gallium, TGSI based "virgl" context.  We only need 1 capset
ID per context type, though virgl has two due a bug that has since
been fixed.

The use case is the "gfxstream" rendering library and upcoming
"venus" renderer.

gfxstream doesn't do Gallium/TGSI translation which requires highp, so
it may have better performance for GLES on GLES emulation.
{gfxstream vk}/{venus} are also required for Vulkan emulation.

The goal is for guest userspace to choose the optimal context type
depending on the situation/hardware.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>

BUG: 173630595
TEST: boot VM

Change-Id: I631756696ac34002186e99179a7a6f2c848b0cc3