ARM: debug-ll: Add support for r8a7992

Enable low-level debugging support for R-Car V2H (r8a7792).
V2H uses SCIF0 for the debug console, like most other R-Car Gen2 SoCs.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>