ext4: add helpers for checking whether quota can be enabled/is journalled

ext4: add helpers for checking whether quota can be enabled/is journalled

Right now, there are several places, where we check whether fs is
capable of enabling quota or if quota is journalled with quite long
and non-self-descriptive condition statements.

This patch wraps these statements into helpers for better readability
and easier usage.

Link: https://lore.kernel.org/r/1603336860-16153-1-git-send-email-dotdot@yandex-team.ru
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Roman Anufriev <dotdot@yandex-team.ru>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>