Update README
Add GRALLOC_USAGE_PRIVATE_UNCACHED to preview window usage
camera: add ION allocation option to native camera HAL

This is port of:
https://www.codeaurora.org/cgit/quic/la/platform/hardware/qcom/camera/commit/?id=5e934f6a59a7b8c30cf9aabdbe2db82ad01f71d9
Camera: Fix for camcorder preview freeze

stopPreviewInternal() in stopRecording() is no longer needed for 7x27A in ICS
CRs-Fixed: 323165

Change-Id: Ie0bb8221f8b4b629e79f0c704e4b72c3971ee14d
Camera: Enable preview frame callback

This is port of:
https://www.codeaurora.org/cgit/quic/la/platform/hardware/qcom/camera/commit/?id=addc6f3380b7b555d36bedf8580109839298587d
Camera: Use PMEM ADSP heap when ION heap is not used

This is port of:
https://www.codeaurora.org/cgit/quic/la/platform/hardware/qcom/camera/commit/?id=054ac5b7a79bca5d91cf57e42e46e0059e466654
Do not send the stopPreview to lower layers if previewWindow is null