Force default device if MESA_VK_DEVICE_SELECT_FORCE_DEFAULT_DEVICE
environment variable set. This will not give multiple device
options to app. There are apps that selects gpu to use based on its
own criteria, this patch can force default behaviour for these apps
by giving only one gpu device to select from.
v2: return 0 if no physical device present (Mihai Preda)
v3: document environment variables (Mihai Preda)(Marek Olšák)
Signed-off-by: Yogesh Mohan Marimuthu <yogesh.mohanmarimuthu@amd.com>
Reviewed-by: Mihai Preda <mhpreda@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15585>
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