UVC_CONTROL_* flags to UVC_CTRL_FLAG_*

This makes the public driver API more uniform, in preparation of moving
uvcvideo.h to include/linux. Keep the old names for backward
compatibility with existing applications.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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