dload_util: Add normal dload mode entrance

Enum determines if the requested dload mode is emergency or normal.
All dependent function calls are updated respectively.
msm8974 and msm8226 set_download_mode() functions are updated with the
target-specific normal download mode address

Change-Id: I500c1e3c7e835ad6a6fa59ea2701790a7fd12769
9 files changed