graphics: factor out BMP header parsing
graphics: factor out BMP header parsing

todorez/tummiboot,miguelinux/gummiboot2systemd-boot,FrozenCow/gummiboot,liliang365/my_gummiboot,trilean/gummiboot,aaronp24/gummiboot,todorez/tummiboot,freedesktop-unofficial-mirror/gummiboot,liliang365/my_gummiboot,todorez/gummiboot-multiboot2,todorez/gummiboot-multiboot2,miguelinux/gummiboot2systemd-boot,aaronp24/gummiboot,FrozenCow/gummiboot,freedesktop-unofficial-mirror/gummiboot,trilean/gummiboot