This adds basic support for 32bit bitmaps for the SVP backend. For 
other backends the support is disabled for now as we need to add it for 
each backend separately and enable support.

When this patch is applied it is possible to a Bitmap with bit count 
32, but currently no input filter uses this with the exception of the 
new PngImageReader(libpng based), which is used only for the icons.

For a general support more things need to be implemented and tested:
- conversion back and fourth between 32-bit and 24-bit + 8bit alpha (or 
other supported pairs) 
- 'raw' export of the bitmap needs to be handeled properly (like in
SVM import/export) so it creates the correct image.
- input filters need to be checked and converted if this is necessary
- look for possible bugs when drawing transparent bitmaps
- check of UNO API

Change-Id: I7a7be0e6134dfdd9a7aeaef897131bb6e710ae7e
Reviewed-on: https://gerrit.libreoffice.org/69289Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
Tested-by: Tomaž Vajngerl <quikee@gmail.com>