pm2: Power Management driver changes for 8x25

Current pm2.c driver supports low power mode functionality
only for single APPS processor targets. This patch adds extra
functionality to pm2.c driver to support multicore APPS
processor targets where MODEM is a master.

These changes makes pm2.c driver backward compatible to
older targets(eg: 7x27a & 7x30 etc) & multicore APPS
processors like 8x25.

Change-Id: I79b23b2a2052aa55f9a169886dea17180614dedb
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>