Vulkan: load built-in driver into default namespace as a fallback

There isn't sphal in vendor config because the default has the same
access there. This change allows vendor processes to load Vulkan driver
into the default namespace.

Bug: 170258171
Test: Vulkan driver can be loaded into vendor processes
Change-Id: If58493e6954e4e8d2309aaca392fcdffea9c6b9a
Merged-In: If58493e6954e4e8d2309aaca392fcdffea9c6b9a
(cherry picked from commit 40e84f1f)