regulator: cpr3-hmss-regulator: configure retention voltage based on fuses

Add support to determine the HMSS retention voltage based on
data read from hardware fuses. In particular, the CPU retention
voltage is defined to be the maximum of the VDD_MX and VDD_APCC retention
voltages, both of which are available in the fuse region. Read these
fuses and configure the LDO retention regulator to the HMSS retention
voltage when the CPR3 HMSS regulator driver probes.

Change-Id: If5e319f3b4395d4a4a230e900e545e5ec9e78eba
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>