i2c: qcom-geni: add desc struct to prepare support for I2C Master Hub variant

The I2C Master Hub is a stripped down version of the GENI Serial Engine
QUP Wrapper Controller but only supporting I2C serial engines without
DMA support.

Those I2C serial engines variants have some requirements:
- a separate "core" clock
- doesn't support DMA, thus no memory interconnect path
- fixed FIFO size not discoverable in the HW_PARAM_0 register

Add a desc struct specifying all those requirements which will be used in
a next change when adding the I2C Master Hub serial engine compatible.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>