mfd: dbx500: Export prmcu_request_ape_opp_100_voltage

This function needs to be exported to let clients be able to
request the ape opp 100 voltage.

Cc: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>