i965: protect bo_reuse access with the bufmgr lock

Fixes a possible data race spotted while debugging on other EGL related failures where glFinish and eglCreateContext are going on at the same time:

  ==11558== Possible data race during read of size 1 at 0x5E78CD0 by thread #23
  ==11558== Locks held: 1, at address 0x5E77CA8
  ==11558==    at 0x61B71D4: bo_alloc_internal (brw_bufmgr.c:639)
  ==11558==    by 0x61B7328: brw_bo_alloc (brw_bufmgr.c:669)
  ==11558==    by 0x61EF975: recreate_growing_buffer (intel_batchbuffer.c:231)
  ==11558==    by 0x61EFAAE: intel_batchbuffer_reset (intel_batchbuffer.c:255)
  ==11558==    by 0x61EFB85: intel_batchbuffer_reset_and_clear_render_cache (intel_batchbuffer.c:280)
  ==11558==    by 0x61F0507: brw_new_batch (intel_batchbuffer.c:551)
  ==11558==    by 0x61F12C1: _intel_batchbuffer_flush_fence (intel_batchbuffer.c:888)
  ==11558==    by 0x61BDD6B: intel_glFlush (brw_context.c:296)
  ==11558==    by 0x61BDDB9: intel_finish (brw_context.c:307)
  ==11558==    by 0x623831B: _mesa_Finish (context.c:1906)
  ==11558==    by 0x46D556: deqp::egl::GLES2ThreadTest::Operation::execute(tcu::ThreadUtil::Thread&)
  ==11558==    by 0x721502: tcu::ThreadUtil::Thread::run()
  ==11558==
  ==11558== This conflicts with a previous write of size 1 by thread #26
  ==11558== Locks held: 1, at address 0x5D09878
  ==11558==    at 0x61B98A9: brw_bufmgr_enable_reuse (brw_bufmgr.c:1541)
  ==11558==    by 0x61BF09D: brw_process_driconf_options (brw_context.c:854)
  ==11558==    by 0x61BF6CA: brwCreateContext (brw_context.c:993)
  ==11558==    by 0x621181F: driCreateContextAttribs (dri_util.c:473)
  ==11558==    by 0x53FE87B: dri2_create_context (egl_dri2.c:1388)
  ==11558==    by 0x53EE7BE: eglCreateContext (eglapi.c:807)
  ==11558==    by 0x5C8AB9: eglw::FuncPtrLibrary::createContext(void*, void*, void*, int const*) const
  ==11558==    by 0x46E027: deqp::egl::GLES2ThreadTest::CreateContext::exec(tcu::ThreadUtil::Thread&)

Signed-off-by: Tapani Pälli tapani.palli@intel.com