common: increase default x alignment to 16 in phys mem pool

This alignment works better with all blitters

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
common: Clean up confusing and incorrect size alignment names and logs

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
common: Add utility function to base blitter to calculate empty regions

Given an output and a video region (video region always being a subset
of the output region), calculate the empty regions (regions inside the
output but outside the video region).

Blitters need to fill these with black pixels. This new utility function
takes care of calculating the region rectangles.

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
g2d: use gst_imx_base_blitter_calculate_empty_regions() for empty regions

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