1. Introduce a new structure `struct mxc_i2c_bus`, this structure will
   used for non-DM and DM.
2. Remove `struct mxc_i2c_regs` structure, but use register offset to access
   registers based on `base` entry of `struct mxc_i2c_bus`.
3. Remove most `#ifdef I2C_QUIRK_REG`. Using driver_data to contain platform
   flags. A new flag is introduced, I2C_QUIRK_FLAG.
4. Most functions use `struct mxc_i2c_bus` as one of the parameters.
   Make most functions common to DM and non-DM, try to avoid duplicated code.
5. Support DM, but pinctrl is not included. Pinmux setting is still set
   by setup_i2c, but we do not need bus_i2c_init for DM.
6. struct i2c_parms and struct sram_data are removed.
7. Remove bus_i2c_read bus_i2c_write prototype in header file. The frist
   paramter of bus_i2c_init is modified to i2c index. Add new prototype
   i2c_idle_bus and force_bus_idle. Since bus_i2c_init is not good for
   DM I2C and pinctrl is missed, we use a weak function for i2c_idle_bus.
   Board file take the responsibility to implement this function, like this:
   "
   int i2c_idle_bus(struct mxc_i2c_bus *i2c_bus)
   {
	   if (i2c_bus->index == 0)
		   force_bus_idle(i2c_pads_info0);
	   else if (i2c_bus->index == 1)
		   force_bus_idle(i2c_pads_info1);
	   else
		   xxxxxx
   }
   "
8. Introduce a weak function, enable_i2c_clk
9. Tested on an i.MX7 platform. Log info:
 => dm tree
 Class       Probed   Name
 ----------------------------------------
 root        [ + ]    root_driver
 simple_bus  [   ]    |-- soc
 simple_bus  [   ]    |   |-- aips-bus@30000000
 simple_bus  [   ]    |   |   |-- anatop@30360000
 simple_bus  [   ]    |   |   `-- snvs@30370000
 simple_bus  [   ]    |   |-- aips-bus@30400000
 simple_bus  [   ]    |   `-- aips-bus@30800000
 i2c         [   ]    |       |-- i2c@30a20000
 i2c         [   ]    |       `-- i2c@30a40000
 simple_bus  [   ]    `-- regulators
 => i2c dev 0
 Setting bus to 0
 => i2c probe
 Valid chip addresses: 08 50
 => i2c md 8 31
 0031: 08 08 08 08 08 08 08 08 08 08 08 08 08 08 08 08

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Acked-by: Simon Glass <sjg@chromium.org>