compositor-drm: Make unused parts of the cursor image transparent
compositor-drm: Make unused parts of the cursor image transparent

The bo for the cursor image is always created with size 64x64 even if
the actual cursor image is smaller than that. If this memory is not
initialized, random data can create artifacts near the cursor.

Signed-off-by: Ander Conselvan de Oliveira <71330eafc99ba196752d2b2af84b34019e4104c2@intel.com>

eyolfson/weston,udoprog/weston,mchalupa/weston,jonnylamb/weston,sir-murray/weston,Gnurou/weston,giucam/weston,Fantu/compositor-spice,udoprog/weston,Tarnyko/weston-xdg_surface_present,eyolfson/weston,giucam/weston,mchalupa/weston,kwm81/weston,jonnylamb/weston,krezovic/weston,Fantu/compositor-spice,xorgy/weston,Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice,krezovic/weston,sir-murray/weston,xorgy/weston,Gnurou/weston,kwm81/weston