After getting the regmap size from the device tree we should
reduce the ranges to the really available registers. This
allows to read only existing registers from the debug fs
and makes the regmap check out-of-bounds access.

For the jz4780 we have done this already.

Suggested-for: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>