arm: socfpga: socrates: make rtc work

This patch makes the on-board RTC work on the socfpga_socrates board.
This rtc is present on the board, but it does not work (fails with a
timeout).

This patch adds a weak pull-up on the I2C0-SCL pin connected to the m41t82
RTC on this board. While the SDA line has a pull-up on the pcb, the pull-up
on the SCL line seems to be missing. To work around this, enable the
weak-pull-up feature on this pin.

After applying this patch, the rtc timeout is gone and the 'date' command
can access the rtc chip.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>