Revise layer, extension and feature setup for Vulkan

src/gpu/vk/GrVkUtil.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrVkUtil_DEFINED
 #define GrVkUtil_DEFINED
 
 #include "GrColor.h"
 #include "GrTypes.h"
 #include "vk/GrVkInterface.h"
 
 #include "vulkan/vulkan.h"
 
-// the minimum version of Vulkan supported
-const uint32_t kGrVkMinimumVersion = VK_MAKE_VERSION(1, 0, 3);
-
 // makes a Vk call on the interface
 #define GR_VK_CALL(IFACE, X) (IFACE)->fFunctions.f##X;
 // same as GR_VK_CALL but checks for success
 #ifdef SK_DEBUG
 #define GR_VK_CALL_ERRCHECK(IFACE, X) \
     VkResult SK_MACRO_APPEND_LINE(ret) = GR_VK_CALL(IFACE, X); \
     SkASSERT(VK_SUCCESS == SK_MACRO_APPEND_LINE(ret));
 #else
 #define GR_VK_CALL_ERRCHECK(IFACE, X)  (void) GR_VK_CALL(IFACE, X);
 #endif
 
 /**
  * Returns the vulkan texture format for the given GrPixelConfig
  */
 bool GrPixelConfigToVkFormat(GrPixelConfig config, VkFormat* format);
 
 bool GrSampleCountToVkSampleCount(uint32_t samples, VkSampleCountFlagBits* vkSamples);
 
 #endif