intel: Work around differences between C and C++ scoping rules.

intel: Work around differences between C and C++ scoping rules.

In C++, if a struct is defined inside another struct, or its name is
first seen inside a struct or function, the struct is nested inside
the namespace of the struct or function it appears in.  In C, all
structs are visible from toplevel.

This patch explicitly moves the decalartions of intel_batchbuffer to
toplevel, so that it does not get nested inside a namespace when
header files are included from C++.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>