i2c: sprd: Prevent i2c accesses after suspend is called

Add one flag to indicate if the i2c controller has been in suspend state,
which can prevent i2c accesses after i2c controller is suspended following
system suspend.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>