dt-bindings: mmc: Clean-up examples to match documented bindings

dt-bindings: mmc: Clean-up examples to match documented bindings

The "sdhci" compatible is not documented though used as a fallback in a
few cases. It is also not supported by a Linux driver. Just remove the
example as part of ridding examples of undocumented bindings.

The "brcm,bcm43xx-fmac" compatible is also not documented. Update the
example to use one of the correct ones, "brcm,bcm4329-fmac", instead and
use a device class based nodename.

Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: linux-mmc@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210519153712.3146025-1-robh@kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>