[v2] cpuidle: add riscv cpuidle driver

[kernel test robot]

Hi liush,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on pm/linux-next]
[also build test WARNING on linus/master v5.9-rc6 next-20200921]
[cannot apply to daniel.lezcano/clockevents/next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/liush/cpuidle-add-riscv-cpuidle-driver/20200921-161139
base:   https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
config: riscv-allyesconfig (attached as .config)
compiler: riscv64-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=riscv 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp at intel.com>

All warnings (new ones prefixed by >>):

>> drivers/cpuidle/cpuidle-riscv.c:22:12: warning: no previous prototype for 'riscv_low_level_suspend_enter' [-Wmissing-prototypes]
      22 | int __weak riscv_low_level_suspend_enter(int state)
         |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# https://github.com/0day-ci/linux/commit/30d1da9b67239e99038b0bad282b70454865be02
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review liush/cpuidle-add-riscv-cpuidle-driver/20200921-161139
git checkout 30d1da9b67239e99038b0bad282b70454865be02
vim +/riscv_low_level_suspend_enter +22 drivers/cpuidle/cpuidle-riscv.c

    21	
  > 22	int __weak riscv_low_level_suspend_enter(int state)
    23	{
    24		return 0;
    25	}
    26	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
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