logd: klogd and Mediatek

- sniff for PID in kernel log messages if available
- properly deal with klogd watermark in face of modified output
- deal more stringently with priority tag, must have [ following
- suppress process-name stutter in tag that can happen
- do not use : to demark tag if within [ ]

Mediatek-special change that adds <printk_state>(<cpu>)[<pid>:<comm>]
as a prefix to the printk messages. Along the lines of (simplified
for entertainment purposes, YMMV):

    char tbuf[50]; /* printk prefix */
    int this_cpu = smp_processor_id();
    char state = __raw_get_cpu_var(printk_state);
    unsigned tlen = snprintf(tbuf, sizeof(tbuf), "%c(%x)[%d:%s]",
               state, this_cpu, current->pid, current->comm);

Bug: 23517551
Change-Id: I568e25c5aa6d8474835454a0e83b19c2921b7985