arm64: dts: imx8mp: Make MX8MP_I2C_DEFAULT independent on drive strength

arm64: dts: imx8mp: Make MX8MP_I2C_DEFAULT independent on drive strength

Currently MX8MP_I2C_DEFAULT macro includes a fixed drive
strength (MX8MP_DSE_X6) thus limiting its use to only I2C
pins that require X6 drive.

There are many pinctrl configurations for I2C that use different
drive strength while still using the common I2C default configurations
(pull-up, Schmitt input, pull enable, SION).

So make the MX8MP_I2C_DEFAULT macro more flexible and reusable by removing
DSE_X6 drive strength from it's definition but add or it in all places
it is necessary.

Reviewed-by: Maud Spierings <maudspierings@gocontroll.com>
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>