i2c: i2c-bfin-twi: add CONFIG_PM_SLEEP to suspend/resume functions

Add CONFIG_PM_SLEEP to suspend/resume functions to fix the following
build warning when CONFIG_PM_SLEEP is not selected. This is because
sleep PM callbacks defined by SIMPLE_DEV_PM_OPS are only used when
the CONFIG_PM_SLEEP is enabled.

drivers/i2c/busses/i2c-bfin-twi.c:585:12: warning: 'i2c_bfin_twi_suspend' defined but not used [-Wunused-function]
drivers/i2c/busses/i2c-bfin-twi.c:600:12: warning: 'i2c_bfin_twi_resume' defined but not used [-Wunused-function]

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>