drivers: lpm-levels: Update the RIMPS register pasring from DT

This patch adds the logic to get the RIMPS address with passing
domain name and stores the rimps address to lpm_cpu structure so
that it can access from the last core of corresponding cluster
domain going to rail-pc to program the RIMPS timer value.

Change-Id: I90418d280440e3f26615583454116c01cec04126
Signed-off-by: Raghavendra Kakarla <rkakarla@codeaurora.org>