Added cpu-keepalive methods

Applications can block suspend via:
 MCE_CPU_KEEPALIVE_PERIOD_REQ
 MCE_CPU_KEEPALIVE_START_REQ x N
 MCE_CPU_KEEPALIVE_STOP_REQ

And dsme can signal wakeup from suspend via:
 MCE_CPU_KEEPALIVE_WAKEUP_REQ
Updated mce version to @since 1.12.8

The mce 1.12.7 was released without cpu-keepalive plugin.
Merge pull request #2 from spiiroin/cpu_keepalive_methods

Added cpu-keepalive methods
Updated changelog
Finish mce-dev 1.12.3