svga: only destroy render target view from a context that created it

svga: only destroy render target view from a context that created it

A texture can be destroyed from a different context from which it is
created, but destroying the render target view from a different context
will cause svga device errors. Similar to shader resource view,
this patch skips destroying render target view or depth stencil view
from a non-parent context.

Fixes driver errors running NobelClinician Viewer application.

Tested with NobelClinician Viewer, MTT piglit, glretrace.

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