MIPS: Add support for full dynticks CPU time accounting

With the correct cmpxchg64 on 32-bit platforms, we can now add the config
HAVE_VIRT_CPU_ACCOUNTING_GEN into arch/mips/Kconfig.

Signed-off-by: Deng-Cheng Zhu <dengcheng.zhu@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: macro@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9475/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>