drm/vmwgfx: add support for updating only offsets of constant buffers

This adds support for the
SVGA_3D_CMD_DX_SET_VS/PS/GS/HS/DS/CS_CONSTANT_BUFFER_OFFSET commands (which only update
the offset, but don't rebind the buffer), which saves some overhead.

Signed-off-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Charmaine Lee <charmainel@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211206172620.3139754-11-zack@kde.org