v3d: Don't force SCANOUT for PIPE_BIND_SHARED requests

This was workaround for the users of gbm_bo_create_with_modifiers(),
which were unable to specify the buffer usage (GPU / GPU+DISPLAY).

But after the commit [1] this become possible. And forcing usage to
GBM_BO_USE_SCANOUT migrated directly into gbm_bo_create_with_modifiers(),
allowing us to remove such workarounds from the drivers [2].

This makes possible to allocate the buffers in VRAM using
gbm_bo_create_with_modifiers2 and gbm_bo_create and providing correct use
flag, saving CMA memory.

This should also enable tiling for such buffers.

1: 268e12c6 ("gbm: add gbm_{bo,surface}_create_with_modifiers2")
2: ad50b47a ("gbm: assume USE_SCANOUT in create_with_modifiers")

This patch was extracted from !12402 (closed) with reworded message and proper justification.