const_structs.checkpatch: add regmap structs

Many structs used by regmap should be const by default.
Add entries to const_structs.checkpatch for them for checkpatch.pl to
warn on new non-const additions.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://patch.msgid.link/20240706-regmap-const-structs-v1-1-d08c776da787@weissschuh.net


Signed-off-by: Mark Brown <broonie@kernel.org>