logging: add support for 64 bit timestamps with Linux format

Combining CONFIG_LOG_OUTPUT_FORMAT_LINUX_TIMESTAMP and
CONFIG_LOG_TIMESTAMP_64BIT results in a wrong timestamp, as the
Linux timestamp format print call assumes a 32 bit variable for
the seconds. Fix it by using a different print format for 64 bit
timestamps.

Fixes: #55372

Signed-off-by: Martin Sollie <ms@aziwell.no>