[MIPS] Au1xx0: really set KSEG0 to uncached on reboot

Fix a really old buglet in AMD Au1xx0 restart code: instead of
modifying the whole CP0 Config.K0 field to 010b (meaning KSEG0 uncached)
before flushing the caches and resetting a board, it only sets bit 1 of that
reg. which is effectively a NOP since Config.K0 == 011b as the kernel sets it
up (which is also its default value for Au1xx0).

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>