Support VK_KHR_portability_enumeration

Support VK_KHR_portability_enumeration

The portability enumeration extension needs to be enabled if it is
present to allow for CTS to enumerate portability devices.

This commit refactors createDefaultInstance so that it only enumerates
the available instance extensions once instead of twice.

It fixees #3644 by adding VK_KHR_portability_enumeration to the list
of known extensions with the addition of a corresponding json file.

Components: Vulkan

Affected Tests:
All vulkan tests

Change-Id: Ib828ee9f385f2eb2e68e03a6b3b3632443da10df