sparc, leon: sparc-leon specific SRMMU initialization and bootup fixes.

The sparc-leon caches are virtually tagged so a flush is needed on ctx
switch.

Signed-off-by: Konrad Eisele <konrad@gaisler.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>