dt-bindings: arm: rockchip: Add gru-scarlet sku{2,4} variants

The Gru-Scarlet family includes a variety of SKU identifiers, using
parts of a 3-bit space {0..7}. SKU2 and SKU4 devices (under a few
different manufacturer names) also use the Innolux display.

For reference, the original vendor tree source:

CHROMIUM: arm64: dts: rockchip: add sku{0,2,4} compatibility
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/f6ed665c9e2eb37fb2680debbb36ec9fb0e8fb97

CHROMIUM: arm64: dts: rockchip: scarlet: add SKU0 device tree
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/9987c8776f4b087d135d761e59f7fa6cc83fc7fc



Signed-off-by: Brian Norris <briannorris@chromium.org>
Link: https://lore.kernel.org/r/20220817123350.1.Ibb15bab32dbfa0d89f86321c4eae7adbc8d7ad4a@changeid


Signed-off-by: Heiko Stuebner <heiko@sntech.de>