DS3231 Alarm features

[gKits]

It seems the original PR #758 was abandoned by @mfulz.

I tried to contact them and contribute the missing Alarm2 features to their PR but sadly I got no response.
Therefore I forked their fork and added the proposed changes in #758.

This PR adds:

• Alarm1 set, enable, read
• Alarm2 set, enable, read
• SQW set, read for interrupts

[deadprogram]

Hello @gKits thanks for picking up on this work.

Perhaps you might want to replace the legacy package calls with the new regmap package, to avoid heap allocations.

Please see https://github.com/tinygo-org/drivers/blob/dev/internal/regmap/i2c-spi.go#L67

What do you think?

[gKits]

@deadprogram Sure can do. I used the regmap package everywhere I could. Only in SetTime and SetAlarm2 I used the Tx method of the bus directly because there I need to write chunks of data that would require more than 1 write because they have an odd number of bytes.

Maybe the regmap.Device8I2C type could provide a fitting WriteData method for the already existing ReadData method in the future?