drivers: i2c: mxc: Fix compiler error when using i2c dm mode

drivers: i2c: mxc: Fix compiler error when using i2c dm mode

I2C dm mode enablemenet causes below compilation errors:

In file included from include/config.h:8:0,
                 from include/common.h:20:
include/config_fallbacks.h:51:4: error: #error "Cannot define
CONFIG_SYS_I2C when CONFIG_DM_I2C is used"
 #  error "Cannot define CONFIG_SYS_I2C when CONFIG_DM_I2C is used"
    ^~~~~
In file included from include/config.h:8:0,
                 from include/common.h:20:
include/config_fallbacks.h:51:4: error: #error "Cannot define
CONFIG_SYS_I2C when CONFIG_DM_I2C is used"
 #  error "Cannot define CONFIG_SYS_I2C when CONFIG_DM_I2C is used"
    ^~~~~

board/freescale/lx2160a/lx2160a.c: In function 'board_early_init_f':
board/freescale/lx2160a/lx2160a.c:108:2: warning: implicit declaration
of function 'i2c_early_init_f'; did you mean 'arch_early_init_r'?
[-Wimplicit-function-declaration]
  i2c_early_init_f();
  ^~~~~~~~~~~~~~~~
  arch_early_init_r

 drivers/i2c/mxc_i2c.c: In function 'mxc_i2c_probe':
  drivers/i2c/mxc_i2c.c:824:8: warning: implicit declaration of function
'enable_i2c_clk';
  did you mean 'enable_irq_wake'? [-Wimplicit-function-declaration]
  ret = enable_i2c_clk(1, bus->seq);
        ^~~~~~~~~~~~~~
        enable_irq_wake

So fix these compilation errors.

Signed-off-by: Chuanhua Han <chuanhua.han@nxp.com>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>