drivers/rtc/rtc-pcf8563.c: introduce read|write_block_data

This functions allow to factorize I2C I/O operations.

Signed-off-by: Vincent Donnefort <vdonnefort@gmail.com>
Cc: Simon Guinot <simon.guinot@sequanux.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>