rtc: rv3029: fix alarm support

The RTC RV3029 handles different types of alarms : seconds, minutes, ...
These alarms can be enabled or disabled individually using an AE_x bit
which is the last bit (BIT(7)) on each alarm registers.

To prepare the alarm IRQ support, the current code enables all the alarm
types by setting each AE_x to 1.
It also fixes others alarms issues :
   - month and weekday errors : it was performing -1 instead of +1.
   - wrong use of bit mask with bin2bcd

Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>