CHROMIUM: i965: Implement EGL_KHR_mutable_render_buffer

Tested with a low-latency handwriting application on Android Nougat on
the Chrome OS Pixelbook (codename Eve) with Kabylake.

BUG=b:77899911
TEST=No android-cts-7.1 regressions on Eve.

Change-Id: Ia816fa6b0a1158f81e5b63477451bf337c2001aa