arm64: dts: renesas: enable HS400 on R-Car Gen3

Successfully tested on H3 ES2.0 and M3-N ES1.0.
Transfer rates where >160MB/s for H3 and >200MB/s for M3-N.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>