This implies to change the interface between the
arch independent gdbserver files and the arch dependent files
as AVX implies a choice of xml files at run time.
In valgrind-low-amd64.c, the xml files and the nr of registers
are different depending on AVX support or not.
Other platforms still have a fully static nr of registers.
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@12581
