spmi-pmic-arb: change mode callback/ops for v3

The v3 arbiter removes the security checks and moves them to SMMU
drivers outside the scope of this driver. So reset the mode call
back for v3 similar to v1.

Change-Id: I043178382cd90515063d09f526bd3e94f8ed5fc3
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>