MIPS: Loongson64: Set timer mode in cpu-probe

Loongson64 C and G processors have EXTIMER feature which
is conflicting with CP0 counter.

Although the processor resets in EXTIMER disabled & INTIMER
enabled mode, which is compatible with MIPS CP0 compare, firmware
may attempt to enable EXTIMER and interfere CP0 compare.

Set timer mode back to MIPS compatible mode to fix booting on
systems with such firmware before we have an actual driver for
EXTIMER.

Cc: stable@vger.kernel.org
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>