ARM: dts: imx7d-pico: Extend peripherals support

This extends the peripherals supported by the imx7d-pico.dtsi. It
adds:

 - I2C2
 - Flexcan (flexcan1 and flexcan2 ports)
 - USDHC1
 - UART (6 and 7 ports)
 - PWM (4 ports)
 - eCSPI3

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>