gdb: update to gdb-7.8.1

Signed-off-by: Stephan Raue <stephan@openelec.tv>
kodi: add patch to dont check for SDL-image at buildtime, only texturepacker needs this

Signed-off-by: Stephan Raue <stephan@openelec.tv>
add new package 'SDL2'

Signed-off-by: Stephan Raue <stephan@openelec.tv>
kodi: build with SDL2 support

Signed-off-by: Stephan Raue <stephan@openelec.tv>