arm64: dts: renesas: Add sdhi2_ds pin group to SDHI2 pinctrl groups

This patch adds definitions for configuration of the power-source,
drive-strength, etc... for the SD2_DS pin for Salvator-X(S) and ULCB
boards.

Signed-off-by: Masaharu Hayakawa <masaharu.hayakawa.ry@renesas.com>
Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
[wsa: fixed for ULCB boards, too]
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>