x86, UV: fix redundant creation of sgi_uv

Impact: fix double entry creation in /proc

There is a collision between two UV functions:
  both uv_ptc_init() and gru_proc_init() try to make /proc/sgi_uv

So move it's creation to a single place: uv_system_init()

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>