regulator: cprh-regulator: add support for MEM ACC threshold voltage

Add support for configuring the memory accelerator (MEM ACC)
threshold voltage and the MEM ACC crossover voltage.
The threshold voltage is used to restrict the floor to ceiling
voltage range of all corners so that they cannot cross the
the MEM ACC threshold voltage due to CPR operation.  The
crossover voltage is set when switching the MEM ACC
configuration.

If specified, the APM and MEM ACC crossover voltages are added
to the array of corners after all true corners.  If both are
specified, then the APM crossover corner is added before the MEM
ACC crossover corner (i.e. last corner = MEM ACC crossover and
second to last corner = APM crossover).

CRs-Fixed: 1088429
Change-Id: I2b9b746071579ba9d4bcdcfb6cb755ca08a73182
Signed-off-by: David Collins <collinsd@codeaurora.org>