system property: property set without time spent asleep

There is a 2s timeout for system property set that currently
uses boot_clock as its clock source. If the system goes to sleep
during a property set, it may erroneously cause the timeout to
be reached as boot_clock increments during sleep. This patch
changes from boot_clock to steady_clock to ignore time spent
asleep when determining this timeout.

bug: 71497234
Test: 1. System service process try to set a system property
      with timeout 2s
      2. At the same time, the system go into sleep mode more
      than 2s
      3. System property set will be ok.

Change-Id: I808b9af16974a0f4de60a4ca30ae64d095a13422