ARM: dts: omap5-uevm: document regulator signals used on the actual board

commit e00c27ef
(ARM: dts: OMAP5: Add Palmas MFD node and regulator nodes)
introduced regulator entries for OMAP5uEVM.

However, currently we use the Palmas regulator names which is used for
different purposes on uEVM. Document the same based on 750-2628-XXX
boards - which is meant to be supported by this dts.

Reported-by: Marc Jüttner <m-juettner@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: J Keerthy <j-keerthy@ti.com>
Acked-by: Benoit Cousson <benoit.cousson@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>