vpu: set minimum number of reserved framebuffers to 3

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
vpu: decoder: added hash table to store unfinished frames

This takes care of decoder delays (= when no output frame is available)

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
Fixed missing gst-fsl => gstreamer-imx renaming

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>