rtc: pcf2127: improve timestamp reading performance

Reading the 7 timetamp registers currently involves reading 25 registers
solely to be able to print the content of the three control registers,
in addition to the 7 timestamp registers. This print never occurs,
unless the user enables dynamic debug in this driver or set
CONFIG_RTC_DEBUG.

Reading the timestamp registers should consist of reading 7
consecutive timestamp registers.

This patch optimize the performance of reading the timestamp registers
by reading 7 consecutive registers instead of 25, and dropping the
print of the control registers.

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20230622145800.2442116-3-hugo@hugovil.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>