dt-bindings: mfd: sprd,sc2731: Include SC2730 regulator bindings

The SC2730 PMIC provides a different set of regulators than SC2731 and
thus requires separate regulator bindings. Allow using them for the
"regulators" node.

Signed-off-by: Otto Pflüger <otto.pflueger@abscue.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20260519-sc2730-regulators-v3-2-5bf0e02507e3@abscue.de
Signed-off-by: Lee Jones <lee@kernel.org>

[ upstream commit: 28ad23ef7f58abc8715e6f6c4255921da98e6acc ]