parisc: enable wide mode early

The idle task might have been allocated above 4GB. With the current code
we cannot access that memory because the CPU is still running in narrow
mode.
This was found on a J5000 machine and the patch is required to enable
SPARSEMEM on that machine.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Helge Deller <deller@gmx.de>