Enable TARGET_DISPLAY_INSECURE_MM_HEAP

https://github.com/CyanogenMod/android_hardware_qcom_display-caf/commit/60ccbaec1c8355916ef388007485b8c8e64d0b34

Also removes BOARD_CAMERA_USE_MM_HEAP as it's a deprecated flag

Change-Id: I8540649f62e5c730605fad4a694959bcc8b5be45