arm64: dts: qcom: sdm845: create common zap-shader node

arm64: dts: qcom: sdm845: create common zap-shader node

In order to reduce duplication, move common GPU memory configuration
from individual board files to sdm845.dtsi.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Reviewed-by: David Heidelberg <david@ixit.cz>
Link: https://lore.kernel.org/r/20251028-dt-zap-shader-v1-2-7eccb823b986@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>