Add automatic generation of mipmaps to Vulkan

src/gpu/vk/GrVkCaps.cpp

Index: src/gpu/vk/GrVkCaps.cpp
diff --git a/src/gpu/vk/GrVkCaps.cpp b/src/gpu/vk/GrVkCaps.cpp
index 5b62a3767cc1ec2678717519959e4b2f81f9e04b..b0f3acffb403165fdef79425cb83d1908003c8b4 100644
--- a/src/gpu/vk/GrVkCaps.cpp
+++ b/src/gpu/vk/GrVkCaps.cpp
@@ -20,7 +20,7 @@ GrVkCaps::GrVkCaps(const GrContextOptions& contextOptions, const GrVkInterface*
     /**************************************************************************
     * GrDrawTargetCaps fields
     **************************************************************************/
-    fMipMapSupport = false; //TODO: figure this out
+    fMipMapSupport = true;   // always available in Vulkan
     fNPOTTextureTileSupport = false; //TODO: figure this out
     fTwoSidedStencilSupport = false; //TODO: figure this out
     fStencilWrapOpsSupport = false; //TODO: figure this out