MIPS: Lemote 2F: Add cs5536 MFGPT timer support

MIPS: Lemote 2F: Add cs5536 MFGPT timer support

CPUFreq support for Loongson 2F requires an external timer.

Because the frequency of the MIPS Timer is related to the CPU frequency
which itself is variable another timer of constant frequency is required.

Export the mfgpt0 counter disable / enable operations for the coming
suspend support to suspend / resume the timer.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: cpufreq@vger.kernel.org,
Cc: Dave Jones <davej@redhat.com>,
Cc: Dominik Brodowski <linux@dominikbrodowski.net>,
Cc: yanh@lemote.com
Cc: huhb@lemote.com,
Patchwork: http://patchwork.linux-mips.org/patch/658/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>