MIPS: Loongson: Add CPU_LOONGSON2F_WORKAROUNDS

MIPS: Loongson: Add CPU_LOONGSON2F_WORKAROUNDS

As documented in the  Loongson 2F User Manual [2, 3], the old Loongson2F
series (2F01 / 2F02) have the NOP & JUMP issues which requires workarounds
in the kernel and binutils.  This issue has been rectified in Loongson 2F
series 2F03 so no workarounds needed.

Now that the workarounds [1] adding the the -mfix-loongson2f-nop and
-mfix-loongson2f-jump options have been comitted to the binutils the CVS
repository), we can add the workarounds in the kernel.

The workarounds have no significant side effect on the system but may
decrease performance so we control them through a a new
CPU_LOONGSON2F_WORKAROUNDS config option allowing the users to only enable
it as necessary.

[1] "Fixups of Loongson2F" patch for binutils(actually for gas)
    http://sourceware.org/ml/binutils/2009-11/msg00387.html
[2] Chapter 15 of "Loongson2F User Manual"(Chinese Version)
    http://www.loongson.cn/uploadfile/file/200808211
[3] English Version of the above chapter 15
    http://groups.google.com.hk/group/loongson-dev/msg/e0d2e220958f10a6?dmode=source

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips <linux-mips@linux-mips.org>
Patchwork: http://patchwork.linux-mips.org/patch/1105/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>