i2c: pxa: add OF support

Append these properties in below.
mrvl,i2c-polling
mrvl,i2c-fast-mode

Still keep slave, slave_addr and class in platform data.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>