framebuffer: Fix font background

The background color for font rendering was not properly converted to
the framebuffer format, causing wrong colors to be used.

Signed-off-by: Guillaume Clement <gclement@baobob.org>
framebuffer: Introduce static inline methods for color conversions

Static inline methods allow typesafe functions while keeping the zero
overhead of macros.

Signed-off-by: Guillaume Clement <gclement@baobob.org>
framebuffer: Replace color conversion macros with inline functions.

This allows clearer error messages, etc.

Signed-off-by: Guillaume Clement <gclement@baobob.org>
desco: Add log messages in the framebuffer

These logs show how we can display some text to debug things directly
on the device.

Signed-off-by: Guillaume Clement <gclement@baobob.org>