mm/damon/core: split out quota goal related fields to a struct

'struct damos_quota' is not small now.  Split out fields for quota goal to
a separate struct for easier reading.

Link: https://lkml.kernel.org/r/20240219194431.159606-8-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>