Make compiling the amd vulkan memory allocator optional.

Change-Id: I79b9f78b52f215076a371cbd0ff057d61dd855f0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/285380
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
6 files changed