Add pinmux configurations for MII based CPSW ethernet to am335x-bone.

Default mode is nothing but the values required for the module during
active state. With this configurations module is functional as
expected.

Sleep mode is nothing but the values required for the module during
inactive state. The pins are configured to its reset state to optimize
energy usage for the pins for the suspend/resume cycle
Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>