f2fs: support passing down write hints to block layer with F2FS policy

f2fs: support passing down write hints to block layer with F2FS policy

Add 'whint_mode=fs-based' mount option. In this mode, F2FS passes
down write hints with its policy.

* whint_mode=fs-based. F2FS passes down hints with its policy.

User                  F2FS                     Block
----                  ----                     -----
                      META                     WRITE_LIFE_MEDIUM;
                      HOT_NODE                 WRITE_LIFE_NOT_SET
                      WARM_NODE                "
                      COLD_NODE                WRITE_LIFE_NONE
ioctl(COLD)           COLD_DATA                WRITE_LIFE_EXTREME
extension list        "                        "

-- buffered io
WRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
WRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
WRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_LONG
WRITE_LIFE_NONE       "                        "
WRITE_LIFE_MEDIUM     "                        "
WRITE_LIFE_LONG       "                        "

-- direct io
WRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
WRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
WRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET
WRITE_LIFE_NONE       "                        WRITE_LIFE_NONE
WRITE_LIFE_MEDIUM     "                        WRITE_LIFE_MEDIUM
WRITE_LIFE_LONG       "                        WRITE_LIFE_LONG

Many thanks to Chao Yu and Jaegeuk Kim for comments to
implement this patch.

Signed-off-by: Hyunchul Lee <cheol.lee@lge.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>