init: logd: Allow Developer settings to adjust logd size

- AID_SYSTEM can set persist.logd.size
- AID_SYSTEM can issue command to /dev/socket/logd to
  change the runtime global log sizes.
- Add support for ro.logd.size.* as populated by BoardConfig.mk
- Limit size to maximum ~3% of physical memory.

Bug: 14563261
Bug: 14627052
Change-Id: I606420db2e9d9d032296e71149e4a5b20cbd1137