ARM: dts: r8a77470: Add SDHI0 support

RZ/G1C comes with two different types of IP for the SDHI
interfaces, SDHI0 and SDHI2 share the same IP type, and
such an IP is also compatible with the one found in R-Car
Gen2. SDHI1 IP on the other hand is compatible with R-Car
Gen3 with internal DMA.
This patch completes the SDHI support of the R-Car Gen2
compatible IPs, including fixing the max-frequency
definition of SDHI2, as it turns out there is a bug in
Section 1.3.9 of the RZ/G1C Hardware User's Manual (Rev.
1.00 Oct. 2017).

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>