i2c: mlxcpld: Add support for I2C bus frequency setting

Add support for I2C bus frequency setting according to the specific
system capability. This capability is obtained from CPLD frequency
setting register, which could be provided through the platform data.
If such register is provided, it specifies minimal I2C bus frequency
to be used for the devices attached to the I2C bus. Supported
freqeuncies are 100KHz, 400KHz, 1MHz, while 100KHz is the default.

Signed-off-by: Vadim Pasternak <[email protected]>
Signed-off-by: Wolfram Sang <[email protected]>