Add support for NXP pcf85263 real-time clock. pcf85263 rtc is compatible
with pcf85363,except that pcf85363 has additional 64 bytes of RAM.

1 byte of nvmem is supported and exposed in sysfs (# is the instance
number,starting with 0): /sys/bus/nvmem/devices/pcf85x63-#/nvmem
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>