Add FIND7 to assert list

Stock Oppo recovery uses FIND7. To allow custom recoveries to
install official OTAs, recovery must identify the device as a
FIND7 and the assert is case sensitive.

Change-Id: I7e78c43f1bc18cc866db466a06c047600339000d

Conflicts:
	BoardConfig.mk
find7: Fix typo in device-proprietary-files.txt

Change-Id: I346f188cce48f0dcf590d59596ab749191680306
find7: Remove duplicate properties

Change-Id: I0c70e3b831d9349109f1098e8f0405c030fb3947