ramips: update i2c drivers

ramips: update i2c drivers

* add rt_i2c structure to store driver data
* rewrite read/write check function and add i2c error status check.
  so we don't need to wait until time out.
* add 10 bits address support. according to the data sheet i think
  it is possible. but i haven't verify it.
* the most important is start transfer only need once. otherwise
  it cause I2C_STARTERR status.
* add set i2c clock speed register by dts options "clock-frequency".
  not just hard code it.
* add mt7621 i2c driver. i just copy i2c-ralink.c and change register
  names. and the hardware don't support error status. so i remove it.
  but the logic is the same.

Signed-off-by: Michael Lee <igvtee@gmail.com>