dt-bindings: mmc: sdhci-of-arasan: Add deprecated message for AM65

Commit 26a4f38d ("dt-bindings: mmc: sdhci-of-arasan: Add new
compatible for AM654 MMC PHY") added a new compatible for supporting
controllers on TI's AM65x SOCs. It turns out that the controller is
not compatible with the arasan driver's phy and consumer model as it
requires some phy registers for core sdhci functionality. This calls
for the binding to branch out to a new driver.

Therefore, add a deprecated message for the ti,am654-sdhci-5.1 binding.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>