arm64: dts: Add SDHCI DT node for NS2

The IPROC SDHCI driver works fine for SDIO 3.0 on NS2 so let's enable
it for NS2 SoC in NS2 DT.

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Reviewed-by: Vikram Prakash <vikramp@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>