Disable use of directly wrapping msaa RTs on Vulkan

Currently the Vulkan backend is set up to always treat the "resolve"
target as the main VkImage in a render target and the msaa is a side cart
image. This makes it difficult to just wrap an msaa image that we don't own.
However, unlike GL the equivalent FBO 0 will never be multisampled so there
isn't much use for the functionality. Once we find a need for it we can find
a way to refactor to make it work.

Bug: skia:
Change-Id: I121e9c72a70c2a6f1aaddba2dbae19d8bddc3998
Reviewed-on: https://skia-review.googlesource.com/13980
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
2 files changed