ARM: OMAP3: kill omap3_pmic_get_config and twl_{get,set}_voltage

Last user of these functions was removed in commit
e92fc4 ("ARM: OMAP2+: Drop legacy board file for LDP") during
legacy board file removal.

Signed-off-by: Nicolae Rosia <Nicolae_Rosia@mentor.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>