zram: optimize memory operations with clear_page()/copy_page()

zram: optimize memory operations with clear_page()/copy_page()

Some architectures provides architecture-specific, optimized version of
clear_page()/copy_page(), which may have better performance than
memset()/memcpy(). So use clear_page()/copy_page() to optimize zram
performance if possible.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 42e99bd975fdd24d2bf1a24ebb8b0b42bab8ba65)
Signed-off-by: Alex Shi <alex.shi@linaro.org>