devfreq: memlat: Fix macros to support 32 bit kernels

Cast MBYTE macro to unsiged long instead of unsigned long long.
Unsigned long long causes division errors when used for 32 bit
kernels. Also, add a new macro for Mbps to icc conversion
without loss of precision.

Change-Id: I584869c510d614e47ab7090a1f328df307d412a8
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>