Add helper macro to set the min and max value of the register range.

This is useful when initialising the register ranges of the device like

static const struct regmap_range readable_ranges[] = {
	regmap_reg_range(DEVICE_REG0, DEVICE_REG10),
};
Signed-off-by: NLaxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: NMark Brown <broonie@linaro.org>