Add gyp define to enable vulkan debug layers

On Debug vulkan bots, running with the debug layers on seems to be adding
more than an hour to the total running time. Since we suppress any output
on the bots anyways the debug layers are serving no purpose. Thus I am
adding a gyp define to disable the layers on the bot.

With this change, by default when running vulkan in Debug, the debug_layers
will be enabled. The bots should disable the layers. Android framework
should also have them disabled by default.

TBR=djsollen@google.com

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2185953003

Review-Url: https://codereview.chromium.org/2185953003
12 files changed