xa: fix segfault

Fixes:

  Program received signal SIGSEGV, Segmentation fault.
  bind_samplers (comp=0x21b054, comp=0x21b054, ctx=0x211430)
      at ../../../../../src/gallium/state_trackers/xa/xa_composite.c:445
  445						mask_pic->srf->tex->format);
  (gdb) bt
  #0  bind_samplers (comp=0x21b054, comp=0x21b054, ctx=0x211430)
      at ../../../../../src/gallium/state_trackers/xa/xa_composite.c:445
  #1  xa_composite_prepare (ctx=0x211430, comp=comp@entry=0x21b054)
      at ../../../../../src/gallium/state_trackers/xa/xa_composite.c:488
  #2  0xb6f454b4 in XAPrepareComposite (op=<optimized out>, pSrcPicture=<optimized out>,
      pMaskPicture=<optimized out>, pDstPicture=<optimized out>, pSrc=0x5b3ad8, pMask=0x0,
      pDst=0x5923b8) at msm-exa-xa.c:533

We can't yet handle solid fill mask, so explicitly reject that, rather
than segfaulting.  Otherwise DDX would need to check XA version to see
if solid fill mask were supported.

Signed-off-by: Rob Clark <robclark@freedesktop.org>
nv50,nvc0: add X8Z24_UNORM, fix stencil-only formats

S8_UINT will become useful when ARB_texture_stencil8 becomes supported by
mesa. The other stencil formats are needed for ARB_stencil_texturing.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
mesa/st: implement ARB_stencil_texturing

If StencilSampling is enabled on the texture object, pass in an
equivalent stencil-only format.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
docs: mark ARB_stencil_texturing as done for nv50+/r600+

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
st/egl: Flush resources before presentation (android - bug 77966)

[olv: Use the real name provided by the patch author.  Ideally this could be
moved to somewhere higher level so that we would not need to create a pipe
context to flush resources.  Plus, it is not clear if flushing resources for
another context is valid.]

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>