MediaVulkanGpuTest: use AIMAGE_FORMAT_PRIVATE.

In the use case ImageReader does not need to enforce the color
format, therefore use PRIVATE (opaque) format.

Bug: 380386975
Test: atest android.graphics.cts.MediaVulkanGpuTest
(cherry picked from https://android-review.googlesource.com/q/commit:bc727d3d0c56c1cf54154de10f9d9f5a1a1207d2)
Merged-In: I7bbfd4a5bfa107cce1e2770f26d0e742094fa4ab
Change-Id: I7bbfd4a5bfa107cce1e2770f26d0e742094fa4ab
1 file changed