[PATCH v2] RTC/PCF85063: fix reading/setting time/date

[Juergen Borleis]

The PCF85063 RTC needs special treatment while setting or reading the
time/date:

 - when reading the 7 time/date registers they are blocked from updating by
   the 'one second' pulse internally. So reading all time/date registers
   should happen in one turn to ensure reading is an atomic operation

 - to let setting the time/date be an atomic operation as well, the clock
   dividers must be kept in reset state to avoid a 'one second' pulse during
   writing the 7 time/date registers

Changes from v1:

 - using high level I2C access functions instead of the low level i2c_transfer()
   to simplify the code

Comments are welcome
Juergen

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