parisc: Implement __get/put_kernel_nofault()

Remove CONFIG_SET_FS from parisc, so we need to add
__get_kernel_nofault() and __put_kernel_nofault(), define
HAVE_GET_KERNEL_NOFAULT and remove set_fs(), get_fs(), load_sr2(),
thread_info->addr_limit, KERNEL_DS and USER_DS.

The nice side-effect of this patch is that we now can directly access
userspace via sr3 without the need to use a temporary sr2 which is
either copied from sr3 or set to zero (for kernel space).

Signed-off-by: Helge Deller <deller@gmx.de>
Suggested-by: Arnd Bergmann <arnd@kernel.org>