mfd: Introduce remove_script function for twl4030

New function twl4030_remove_script(u8 flags) takes a script type as
defined in twl.h and prevents any script already loaded in that position
from running.  This is accomplished by programming SEQ_ADD_* to 0x3f,
the END_OF_SCRIPT value, where SEQ_ADD_* is determined by flags.

(Future) users of this function include OMAP board files for machines
facing a race condition between sleep and warm reset.

Signed-off-by: Mike Turquette <mturquette@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>