ASoC: sh: fsi: Document SoC-specific bindings

The documentation only mentioned the generic fallback compatible
property.
Add the missing SoC-specific compatible properties, some of which are
already in use.

Also fix a small typo, while we're at it.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/renesas,fsi.txt

 Renesas FSI
 
 Required properties:
-- compatible			: "renesas,sh_fsi2" or "renesas,sh_fsi"
+- compatible			: "renesas,fsi2-<soctype>",
+				  "renesas,sh_fsi2" or "renesas,sh_fsi" as
+				  fallback.
+				  Examples with soctypes are:
+				    - "renesas,fsi2-r8a7740" (R-Mobile A1)
+				    - "renesas,fsi2-sh73a0" (SH-Mobile AG5)
 - reg				: Should contain the register physical address and length
 - interrupts			: Should contain FSI interrupt
 
-- fsia,spdif-connection		: FSI is connected by S/PDFI
+- fsia,spdif-connection		: FSI is connected by S/PDIF
 - fsia,stream-mode-support	: FSI supports 16bit stream mode.
 - fsia,use-internal-clock	: FSI uses internal clock when master mode.