etnaviv: keep track of buffer valid ranges for PIPE_BUFFER

etnaviv: keep track of buffer valid ranges for PIPE_BUFFER

This allows a write to proceed to an uninitialized part of a buffer
even when the GPU is using the previously-initialized portions.

Such a situation can be triggered with the following API usage example:

  glBufferSubData(..., offset, size, data1);
  glDrawArrays(...);
  // append new vertex data
  glBufferSubData(..., offset+size, size, data2);
  glDrawArrays(...);

Same is done for freedreno, nouveau and radeon.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>