MIPS: Loongson-3: Fix SMP_ASK_C0COUNT IPI handler

MIPS: Loongson-3: Fix SMP_ASK_C0COUNT IPI handler

When Core-0 handle SMP_ASK_C0COUNT IPI, we should make other cores to
see the result as soon as possible (especially when Store-Fill-Buffer
is enabled). Otherwise, C0_Count syncronization makes no sense.

BTW, array is more suitable than per-cpu variable for syncronization,
and there is a corner case should be avoid: C0_Count of Core-0 can be
really 0.

Signed-off-by: Huacai Chen <[email protected]>
Cc: Aurelien Jarno <[email protected]>
Cc: Steven J. Hill <[email protected]>
Cc: Fuxin Zhang <[email protected]>
Cc: Zhangjin Wu <[email protected]>
Cc: Huacai Chen <[email protected]>
Cc: [email protected]
Cc: <[email protected]>
Patchwork: https://patchwork.linux-mips.org/patch/12160/
Signed-off-by: Ralf Baechle <[email protected]>