Rockbox

This is a replacement for formerly submitted #699086.

New:
With this patch, time/date-values are stored in the
config_block from [0xa9] to [0xad], which is saved on
the disk.

The time values have got 36bit alltogether:
second (0-59): 6 bit
minute (0-59): 6 bit
hour (0-23): 5 bit
dayofweek (0-7): 3 bit
day (0-31): 5 bit
month (0-12): 4 bit
year (0-99): 7 bit

Now the values are packed in 5 bytes of the config_block.

Known from #699086:
After a power-loss, the values are read from the
config_block and written to the RTC, so there is
immediately a defined status of the clock.

If the config_block is invalid, the time is generated
from the APPSVERSION-string, which is build at
compile-time.

So:
If you just change the batteries, the last time on disk
will be set,
if you change the CONFIG_VERSION, the time you compiled
your ajbrec.ajz will be set.