ext/dfbvideosink: use libshvio instead of software rendering
ext/dfbvideosink: give more color formats which can be converted by libshvio in getcaps()
ext/dfbvideosink: ignore alpha channel in source data

This is a temporal workaround for ARGB8888 data output by VIN.
ext/dfbvideosink: fix array index at the source pc address setting.
dfb-example: support scaling and position change for the display image

This patch supports below.
- change videotestsrc to v4l2src.
- support scaling and position change with the sub surface
  through command options.
dfb-example: force UYVY pixelformat

set a capability for UYVY format between v4l2src and dfbvideosink
if -u option is specified though the commnad argument.
dfb-example: support specifying a display layer with GetDisplayLayer()
dfb-example: add a option for specifying the number of buffers to be enqueud in the v4l2 driver
dfb-example: support video image cropping
dfb-example: change a default value of queue-size for v4l2src

This change is necessary in continuous capturing with VIN driver.
ext/dfbvideosink: enable scaling if libshvio blitting used
ext/dfbvideosink: control image aspect ratio in scaling V3

This adds a boolean option 'keep-aspect-ratio' to ignore image's
aspect ratio in scaling. The default of the option value is TRUE
that means scaling an image with keeping its aspect ratio.

Changes since V2:
- fix missing 'break' in a switch-case statement

Changes since V1:
- make a function to wrap gst_dfbvideosink_center_rect()
ext/dfbvideosink: handle the query of stride-supported

The query of stride-supported is sent for asking whether
dealing with rowstride is supported.
This patch adds the handler for receiving this query.

This is preliminary for using rowstride obtained by caps
to be set to libshvio.
ext/dfbvideosink: use rowstride to render with libshvio

This patch gets rowstride from caps to be set to libshvio.
ext/dfbvideosink: pass a dummy pointer as the 3rd argument of TestConfiguration(), rather than NULL.

This change is a workaround and may be unnessesary for the latest DirectFB.
According to the spec, the third argument may be specified as NULL, but the
current DirectFB doesn't NULL-check the third argument of TestConfiguration()
when running in slave mode.
dfb-example: add a option for ignoring image's aspect ratio
ext/dfbvideosink: compensate for the interpretation difference of colorspace definitions

The interpretation of colorspace definitions are different between
dfbvideosink and libshvio.
XRGB32 is indicated by following definitions each other.
- dfbvideosink: DSPF_RGB32
- libshvio: REN_XRGB32

This patch compensates for this difference when the definitions are
converted in dfb2shvio_format().
ext/dfbvideosink: set mask fields and endianness for the caps negotiation
ext/dfbvideosink: fix creating a caps list

This patch gives priority to blit over libshvio to judge which
colors formats would be available.
Only if an external surface is specified, libshvio would be always
used. Because blit isn't used in this case in gst_dfbvideosink_show_frame().
ext/dfbvideosink: change the order of color formats for the caps negotiation

This patch changes color format lists obtained by get caps function.
This change puts a higher priority on the following formats.
- RGB32
- UYVY