phy: qcom-ufs: remove obsolute PHY drivers

"20nm" and "qrbtc" PHY drivers were only used for development
purpose and no longer needed now. Hence this patch removes it.

Change-Id: I6938cb9d4f191397ad79a60525e336128fee03c0
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>