MLK-9428 dts: imx6sx: optimize can pad settings

Detailed reproduce steps:
1. boot-up to Linux command prompt.
2. send data from CAN device using "candump" command.
3. capture the TXD waveform during transmission.
4. severe overshoot/undershoot is observed (+4.4V ~ -1.2V).

HW team found that the pad setting of the CAN signal pins is not optimized.
In existing BSP, SPEED/DSE/SRE = 10/110/1 is used. They propose change it
to SPEED/DSE/SRE = 00/100/0.

Conflicts:

	arch/arm/boot/dts/imx6sx.dtsi

Signed-off-by: Dong Aisheng <b29396@freescale.com>
(cherry picked from commit 0e0d95bed6937f4846aeda27de4e93bb141be492)
(cherry picked from commit 2914d58e0182795727930fa9f0bd4236ab9ded3c)