ARM: debug-ll: Add support for r7s9210

Enable low-level debugging support for RZ/A2M (r7s9210).

The RZA2MEVB board uses either SCIF2 (SDRAM enabled) or SCIF4 (HyperRAM
only) for the serial console.

Note that "SCIFA" serial ports on RZ/A2 SoCs use a compressed register
layout, hence add support for that to renesas-scif.S.

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