According to the reference manual and the "Pins Tool" from NXP, the
signals for UART1 and UART2 can be muxed to the SAI2 and SAI3 pads
respectively. Let's add the missing options.
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>