arm: dts: vexpress: Fix addressing issues with 'motherboard-bus' nodes

The 'motherboard-bus' node in Arm Ltd boards fails schema checks as
'simple-bus' child nodes must have a unit-address. The 'ranges' handling is
also wrong (or at least strange) as the mapping of SMC chip selects should
be in the 'arm,vexpress,v2m-p1' node rather than a generic 'simple-bus'
node. Either there's 1 too many levels of 'simple-bus' nodes or 'ranges'
should be moved down a level. The latter change is more simple, so let's do
that. As the 'ranges' value doesn't vary for a given motherboard instance,
we can move 'ranges' into the motherboard dtsi files.

Link: https://lore.kernel.org/r/20210819184239.1192395-6-robh@kernel.org
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>