UPSTREAM: exfat: convert exfat_init_ext_entry() to use dentry cache

Before this conversion, in exfat_init_ext_entry(), to init
the dentries in a dentry set, the sync times is equals the
dentry number if 'dirsync' or 'sync' is enabled.
That affects not only performance but also device life.

After this conversion, only needs to be synchronized once if
'dirsync' or 'sync' is enabled.

Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Reviewed-by: Andy Wu <Andy.Wu@sony.com>
Reviewed-by: Aoyama Wataru <wataru.aoyama@sony.com>
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
(cherry picked from commit d97e0606)

Bug: 362138008

Change-Id: Ibef146478f27c5aff2d948a8222834f6d199964b
Signed-off-by: dongliang.cui <dongliang.cui@unisoc.com>