Adjusts the default magnification settings for config_magnification_area

Cnfig flag, config_magnification_area, determines if the device
supports magnification area or not.
If OEM doesn't support magnification area, we should adjust the
magnification capability setting and window magnification prompt
setting.

Bug: 177371954
Test: atest SettingsBackupTest
Change-Id: I67947285eb6a73b8e0e21d1db866c426a0ea49d7