rtc: add NXP PCF2127 support (i2c)

Added support for NXP PCF2127 RTC (i2c).

[akpm@linux-foundation.org: fix typo, fix warnings]
Signed-off-by: Renaud Cerrato <r.cerrato@til-technologies.fr>
Cc: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>