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
(cherry picked from commit ecf8a24fc10398afc8bbec6e94bab25fc605fb4d)

Merged-In: I96efd5234fdcdac3bfcd48b1c3f1eb309db1bb00
Merged-In: If58493e6954e4e8d2309aaca392fcdffea9c6b9a

Change-Id: I96efd5234fdcdac3bfcd48b1c3f1eb309db1bb00