wsi: Basic memory allocation functions

wsi: Basic memory allocation functions

In vulkan, users can give custom host memory allocation functions. In order
to handle this specification correctly, we should be able to know allocator
of an ICD object. (such as VkInstance, VkDevice, ...) To achieve this, ICD
can provide access functions for the allocator or WSI should track
creation/destruction of required vulkan objects. At this time, we simply
ignore user provided allocator and just use standard system allocation
functions from libc.

Change-Id: Ic75050e2a3f8ebc71737b7f83b87aaff451d0b2d