drm/rockchip: vop2: use devm_regmap_field_alloc for cluster-regs

Right now vop2_cluster_init() copies the base vop2_cluster_regs
and adapts the reg value with the current window's offset before
adding the fields to the regmap.

This conflicts with the notion of reg_fields being const, see
https://lore.kernel.org/all/20240706-regmap-const-structs-v1-1-d08c776da787@weissschuh.net/


for reference, which now causes checkpatch to actually warn about that.

So instead of creating one big copy and changing it afterwards,
add the reg_fields individually using devm_regmap_field_alloc().

Functional it is the same, just that the reg_field we're handling
can stay const.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20250218112744.34433-2-andyshrk@163.com