hwpmc: add summary command and further metadata extensions

metadata changes:

• log pmc sample rate with pmcallocate
• log proc flags with thread / process logging to identify user vs kernel threads

fixes:

• use log cpuid to translate event id to event name

Implement rudimentary summary command to track sample
counts by thread and process name within a pmc log.

% make -j4 buildkernel >& /dev/null &
% sudo pmcstat -S unhalted_core_cycles -S llc-misses -O foo sleep 15
% pmc summary foo
cpu_clk_unhalted.thread_p_any:

idle: 138108207162
clang-6.0: 105336158004
sh: 72340108510
make: 8642012963
kernel: 7754011631

longest_lat_cache.miss:

clang-6.0: 87502625
sh: 40901227
make: 5500165
kernel: 3300099
awk: 2000060

% pmc summary -f ~/foo
idx: 278 name: cpu_clk_unhalted.thread_p_any rate: 2000003
idle: 69054
clang-6.0: 52668
sh: 36170
make: 4321
kernel: 3877
hwpmc: proc(7445): 3319
awk: 1289
xargs: 357
rand_harvestq: 181
mtree: 102
intr: 53
zfskern: 31
usb: 7
pagedaemon: 4
ntpd: 3
syslogd: 1
acpi_thermal: 1
logger: 1
syncer: 1
snmptrapd: 1
sleep: 1
idx: 17 name: longest_lat_cache.miss rate: 100003
clang-6.0: 875
sh: 409
make: 55
kernel: 33
awk: 20
hwpmc: proc(7445): 14
xargs: 9
idle: 8
intr: 3
zfskern: 2