Generate GL_RGB565 internal format configs for Android VK. This allows
apps requesting such formats to map to the appropriate corresponding
Android internal pixel format.

Bug: angleproject:2863
Change-Id: I18f119d6554a601037a40db27234bf33e0ada438
Reviewed-on: https://chromium-review.googlesource.com/c/1258083
Commit-Queue: Tobin Ehlis <tobine@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>