zink/loader: bring up zink on Android

First 2 commits update loader, zink and build configs to properly load Vulkan core on Android.

The next couple commits fix a bunch of bugs w.r.t external fencing.

The last commit implements a missing api required by EGL platform android.

Setup:

• use GALLIUM_DRIVERS=zink
• install src/gallium/targets/dri/libgallium_dri.so as zink_dri.so
• requires root or set at build time: setprop mesa.loader.driver.override zink
• (optional) use skiavk: adb shell setprop debug.hwui.renderer skiavk

Test:

• games and benchmarks run normally
• low-latency stylus app using front buffer rendering runs normally
• basic cts run passes

Open issues:

• #7210 (closed) no GL_ARB_instanced_arrays emulation blocks skiagl
  • forcing skiavk unblocks gl games and other custom gl usages
• VK_IMAGE_LAYOUT_PRESENT_SRC_KHR used for WSI atop external memory
• VUID-VkDescriptorSetLayoutCreateInfo-pNext-pNext
• VUID-VkRenderPassBeginInfo-framebuffer-03214
• VUID-VkRenderPassBeginInfo-framebuffer-03215
• UNASSIGNED-CoreValidation-DrawState-InvalidImageLayout

/cc @zmike @anholt