dt-bindings: spi-msm-geni: Define properties for different SPI usecases

qcom,shared_ee specifies that the serial engine is shared between execution
environments.
qcom,shared_se specifies that the serial engine is shared simultaneously
between execution environments. A true multi-EE usecase.
qcom,le_vm specifies that the serial engine is operating in a trusted VM.

Change-Id: I1d05dadbc857fa66e4c4aa1beddc5e2a9cad1cb4