dt-bindings: reserved-memory: Refine 'size' and 'alignment' types

Both 'size' and 'alignment' are single values, but can be 32 or 64 bits.
Use the precise types rather than the 2 32-bit cell encoding.

Link: https://lore.kernel.org/r/20230125221450.3058762-1-robh@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>