Add WSI functions to the loader.

Modify vulkan.api to include the WSI functions.
Add new wsi functions to generation in get_proc_addr.cpp.tmpl
Add bottom entry points because the WSI functions are not exposed in the
driver.

Change-Id: I63c3a099a489496205b0a9eb82c005a5a48642a1
(cherry picked from commit 23b68ac9fcd2df06ffcc25cf8c4f794dd447bbd1)