rtc: remove an unused rk808 driver file

This file is not used anymore, and the current driver
for rtc of the rk808 is rtc-rk808.c

Change-Id: I2e21f56c0a24af9452bc113c28f25a8eaec096f0
Signed-off-by: Randy Li <randy.li@rock-chips.com>

Author: Randy Li