spi: spi-geni-qcom: Set oversampling based on core revision

The oversampling rate of the core is used in clock related computation.
This rate depends on the core revision. Read the core revision to 
determine the oversampling rate.

Change-Id: Ifae791ef0f40acd011b9b19d23ccd77f5aefddd5
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>