i2c-bfin-twi: Use struct dev_pm_ops for power management

Make the Blackfin On-Chip Two Wire Interface driver define its PM
callbacks through a struct dev_pm_ops object rather than by using
legacy PM hooks in struct platform_driver.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>