mx28evk: Disable CONFIG_CMD_I2C

When loading a Freescale 2.6.35 on a mx28evk the following issue is seen:

sgtl5000_hw_read: read reg error : Reg 0x00
Device with ID register 0 is not a SGTL5000

Disabling CONFIG_CMD_I2C makes the sgtl5000 probe to succeed.

Mainline kernel does not show this problem.

Until the real cause is not identified, disable 'CONFIG_CMD_I2C' for the
time being.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>