arm64: dts: renesas: salvator-x(s): Update I2C ch4 clock to 400kHz

Any of the following devices connected to I2C ch4 of the Salvator-X(S)
boards will operate at 400 kHz:

    PCA9654, 9FGV0841, ADV7482WBBCZ, MAX9611, 5P49V5923, 5P49V6901A

This patch updates the clock frequency to 400 KHz.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
[wsa: squashed commits into one]
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>