mfd: Remove obsolete hwacc implementation for db8500-prmcu

This patch removes the obsolete hwacc implementation in the
DB8500 PRCMU driver.

Signed-off-by: Mattias Nilsson <mattias.i.nilsson@stericsson.com>
Reviewed-by: Jonas Aberg <jonas.aberg@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>