fuchsia: Label all exportable images/buffers as sysmem-backed.

On Fuchsia, all Vulkan images and buffers exportable to VMO
handles are sysmem-backed. We should set the "isSysmemBackedMemory"
flag to true, so that clients can get correct memory
requirements for these images and buffers.

TEST=ScenicPixelTest.UseExternalImage on host-gpu and software-gpu.

Change-Id: I28fbb9fb696375ad2c5b956f89a47212969cd3e2
1 file changed