svga: do not unconditionally enable streamout bind flag

svga: do not unconditionally enable streamout bind flag

Currently we unconditionally enable streamout bind flag at
buffer resource creation time. This is not necessary if the buffer
is never used as a streamout buffer. With this patch, we enable
streamout bind flag as indicated by the state tracker. If the buffer
is later bound to streamout and does not already has streamout bind
flag enabled, we will recreate the buffer with
the new set of bind flags. Buffer content will be copied
from the old buffer to the new one.

Tested with MTT piglit, Nature, Tropics, Lightsmark.

v2: Fix bind flags check as suggested by Brian.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>