[LIBS] Add a simple image loader for framebuffer splash screen.

This patch adds a simple image loader, managing only the P6 ppm format with
less that 256 colors, allowing framebuffer splash screen.

Signed-off-by: Jimmy Durand Wesolowski <jimmy.durand-wesolowski@openwide.fr>
Signed-off-by: Anup Patel <anup@brainfault.org>