The Linux bootsplash is a graphical replacement for the 'quiet' boot option, typically showing a logo and a spinner animation as the system starts.
Currently, it is a part of the Framebuffer Console support, and can be found as CONFIG_BOOTSPLASH in the kernel configuration. This means that as long as it is enabled, it hijacks fbcon's output and draws a splash screen instead.
Purely compiling in the bootsplash will not render it functional - to actually render a splash, you will also need a splash theme file. See the example utility and script in tools/bootsplash for a live demo.