watchdog: booke_wdt: clean up status messages

Improve the status messages that are displayed during some operations of the
PowerPC watchdog timer driver.  When the watchdog is enabled, the timeout is
displayed as a number of seconds, instead of an obscure "period".  The "period"
is the position of a bit in a 64-bit timer register.  The higher the value,
the quicker the watchdog timeout occurs.  Some people chose a high "period"
value for the timer and get confused as to why the board resets within a
few seconds.

Messages displayed during open and close are now debug messages, so that they
don't clutter the console by default.  Finally, printk() is replaced with the
pr_xxx() equivalent.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>