dt-bindings: sdhci-omap: Update binding for legacy SoCs

dt-bindings: sdhci-omap: Update binding for legacy SoCs

Let's add compatible values for the legacy SoCs so we can continue
deprecating omap_hsmmc in favor of sdhci-omap driver.

For omap5, we want to have a separate compatible from omap4 for the
additional features available on omap5. AFAIK ti81 can just use the
omap4 compatible.

Cc: devicetree@vger.kernel.org
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20211015104720.52240-2-tony@atomide.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>