[display] Implement new vsync API

This change adds a new vsync event to the display controller API removes
the present signal event. It also changes the behavior of the cursor
position API to clamp the cursor to the display, to sidestep the issue
of how vsync interacts with a cursor that isn't on the display.

Test: display-test, vkcube, vkcube_image_pipe_swapchain
Change-Id: I6f332e3709eef2c6e1c932581024c2149b65a2a1

[intel-i915] Add various default initializers

ZX-2175 #done

Change-Id: I961dc9a316aadaf7b9da23c130be733387de6f65

[intel-i915] Add locking

Change-Id: I067fb1bb9a8db020d8f80272c12ec732cd15238a

[intel-i915] Implement intel-gpu-core protocol

Also change the address type in read_pci_config_16 to uint16_t, to
match the underlying pci API.

Change-Id: Ic16e79939ea5114c545809f993ff7ad1e2e93d86

[zx] Move public zx headers to match naming convention

The zx library provides headers intended for general use, so the
include path should be spelled <lib/zx/foo.h> as per
https://fuchsia.googlesource.com/docs/+/master/development/languages/c-cpp/naming.md.
This moves the headers into the proper location and updates includes to
match.

Change-Id: I6fc9b2a491b5f8b0d270c4dfc77fa4be5739071b

[intel-i915] Refactor interrupts and add vsync

Change-Id: I9645afa3a49fdc9e80c8ddfa61b3c37a8c79a524