devfreq: add support for different ddr types

Target can support different DDR HW versions supporting different
frequencies, add support in DT to update the devfreq nodes
with corresponding frequency mapping based on DDR type supported.

Change-Id: I954ff2b016bc81b50beb933e08f452861b9bea8c
Signed-off-by: Santosh Mardi <gsantosh@codeaurora.org>