arm64: dts: exynos850-e850-96: Specify reserved secure memory explicitly

arm64: dts: exynos850-e850-96: Specify reserved secure memory explicitly

Instead of carving out the secure area in 'memory' node, let's describe
it in 'reserved-memory'. That makes it easier to understand both RAM
regions and particular secure world memory region. Originally the device
tree was created in a way to make sure it was well aligned with the way
LittleKernel bootloader modified it. But later it was found the
LittleKernel works fine with properly described reserved regions, so
it's possible now to define those in a cleaner way.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://lore.kernel.org/r/20241211033027.12985-1-semen.protsenko@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>