sys/log: Add timing option to log command

[kasjer]

This adds entry count to FCB (and log_fcb) so it number of entries in FCB and log based on FCB gen be easily obtained.

Number of entries stored in the log is counted during call to fcb_init() and used simplified strategy where only record length is read and there is not verification of data against CRC but it allows to quickly asses number of records.

Log API is extended to get number of entries in the given log and currently log_fcb has implementation while other logs will return 0.

Shell command log now has additional parameter -t that allows to measure time for log traversal

log -t

or

log -t reboot_log

Signed-off-by: Jerzy Kasenberg [email protected]