dt-bindings: mmc: marvell,xenon-sdhci: Simplify Armada 3700 if/then schema

Properties are supposed to be defined in the top-level schema and then
disallowed in an if/then schema if necessary. Move the "marvell,pad-type"
property to follow this.

"reg" can also be similarly described at the top-level with only the
number of entries restricted in the if/then schema.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Message-ID: <20241113225602.1782573-1-robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>