unicore32 machine related files: add i2c bus drivers for pkunity-v3 soc

unicore32 machine related files: add i2c bus drivers for pkunity-v3 soc

change from original version -- by advice of Jean Delvare
1. remove global variable i2c_reg, replaced by local variables
2. replace ENXIO with ENODEV when no platform resources
3. add adapter->nr assignment before i2c_add_numbered_adapter() call
4. add judgement for i2c_del_adapter() return value
5. release adapter when driver removed
6. add __devexit for puv3_i2c_remove() function
7. modify several names to more appropriated ones

Signed-off-by: Guan Xuetao <gxt@mprc.pku.edu.cn>
Acked-by: Arnd Bergmann <arnd@arndb.de>