arm64: dts: msm8998: add MSM8998 specific compatible

Add new compatible for MSM8998 (compatible with MSM8996) to allow
further customizing if needed and to accurately describe the hardware.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221115125310.184012-3-krzysztof.kozlowski@linaro.org