venus: use linear modifier for legacy common wsi path

Towards the renderer, venus better uses VK_EXT_image_drm_format_modifier
to force linear with tiling modifier and mod_linear. Doing so won't make
any difference on the mesa implementations we care about given we have
required VK_EXT_image_drm_format_modifier for wsi support.

A lucky side effect of this is to allow common wsi to work with host
implementations not supporting dma_buf export.

Signed-off-by: Yiwei Zhang <zzyiwei@chromium.org>
Part-of: <!15993>
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