regulator: rk808: Convert rk805 buck1/2 to use linear range

It looks like linear range is suitable to describe the voltage table
for rk805 buck1/2:

selector 0 ~ 59: 0.7125V with uV_step = 12500
selector 60 ~ 62: 1.8V with uV_step = 200000
selector 63: 2.3V

With this change, then rk805 buck1/2 can reuse rk808_reg_ops_ranges.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Mark Brown <broonie@kernel.org>