mesa: Fix GL_FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE for default framebuffer.

mesa: Fix GL_FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE for default framebuffer.

From section 9.2. Binding and Managing Framebuffer Objects:

"Upon successful return from Get*FramebufferAttachmentParameteriv, if
pname is FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE, then params will contain
one of NONE, FRAMEBUFFER_DEFAULT, TEXTURE, or RENDERBUFFER, identifying
the type of object which contains the attached image."

And then it clarifies further:

"If the value of FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE is NONE, then
either no framebuffer is bound to target; or the default framebuffer is
bound, attachment is DEPTH or STENCIL, and the number of depth or stencil
bits, respectively, is zero"

Currently, if the default framebuffer is bound, we always return
GL_FRAMEBUFFER_DEFAULT for FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE, but
according to the spec, when GL_DEPTH or GL_STENCIL attachments are
the ones being queried, we should return GL_NONE if they don't exist.

Fixes the following dEQP test:
dEQP-GLES3.functional.state_query.fbo.framebuffer_attachment_x_size_initial

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Cc: "10.6" <mesa-stable@lists.freedesktop.org>