Add support for DS1388.

Support for DS1388 is added by extending the DS1337 driver. DS1388 is
similar to DS1337. The time registers are offset by 1 (due to support
for hundreds of seconds), and there is no century bit.
The configuration and trickle charge registers are also different.
Tested on hardware with Freescale P2010 and DS1388.

Signed-off-by: Kenth Eriksson <kenth.eriksson@transmode.com>