[ALPS08693813] Fix boot performance fail issue

1. Fix gpueb sysram last commit index value uninitialized issue
that causes MFG restore last frequency as max frequency when GPU
power on.
2. Disable DVFS when DDK not ready to avoid getting unreasonable
workload value and result in calculating an unreasonable target
frequency.

MTK-Commit-Id: 4a6cfaed05901da2d9a52029f439adf7cceebaa8

CR-Id: ALPS08693813
Feature: GED driver
Change-Id: I0358654941e20c416bf5e44fbc3bebfda6e58fb0
Signed-off-by: Knight Weng <knight.weng@mediatek.com>