vulkan: Add new cast macros for VkIcd types

vulkan: Add new cast macros for VkIcd types

We can't import the latest vk_icd.h because the new header breaks the
Mesa build. This patch defines new casting macros,
ICD_DEFINE_NONDISP_HANDLE_CASTS() and ICD_FROM_HANDLE(), which can
handle both the old and new vk_icd.h, and will prevent the build from
breaking when we update the header.

In the old vk_icd.h, types were defined as:

  typedef struct _VkIcdFoo {
    ...
  } VkIcdFoo;

Commit 6ebba1f6 in the Vulkan loader changed the above to

  typedef {
    ...
  } VkIcdFoo;

because the old definitions violated the C and C++ specs. According to
the specs, identifiers that begins with an underscore followed by an
uppercase letter are reserved. (It's pedantic, I know), See the Github
issue referenced below.

References: https://github.com/KhronosGroup/Vulkan-LoaderAndValidationLayers/issues/7
References: https://github.com/KhronosGroup/Vulkan-LoaderAndValidationLayers/commit/6ebba1f630015af7a78767a15c1e74ba9b23601c
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Cc: mesa-stable@lists.freedesktop.org