liblog: don't cache property size values and move to own file

Don't cache the property size values since they're only queried at the
start of logd and only once during dumpstate.  Initializing
SerializedLogBuffer, which includes all of the logd queries, takes
under 100us without the cache, certainly fast enough that this cache
is unneeded.

Move these functions to their own file in preparation for removing
them from liblog.

Test: log sizes set appropriately
Change-Id: I15a2fd687dcffb4eab2f22ee0825ca86e40cdba3