Add test group for the VK_KHR_protected_memory extension

Add test group for the VK_KHR_protected_memory extension

* Added framework update for the extension.
* Created basic structure for the VK_KHR_protected_memory extension tests.
* Created a ProtectedContext class which contains the required instance and device
  initializations for the protected test cases.
* Created a simple test case(s) where a protected attachment clearing
  on render pass start is tested.

New tests:
* dEQP-VK.protected_memory.attachment.load_op.*

Components: Vulkan, Framework
VK-GL-CTS issue: 118

Change-Id: I42e8b4f05c3a71c1c3bbc56894e33f5a46b735c6