spi: spi_qsd: Merge back throughput improvements done for small transfers

These changes will merge back the enhancemnts done to improve the medium
side transfers. This was reverted temporarily till the fix identified.

Change-Id: Ib7ac92ecefe7ca3ff9f03716c51dc31b8322ee33
Signed-off-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>