It's possible to make configurations on the build process before building a Linux kernel. When it comes to
configurations about kernel modules, we have three options for each kernel module regarding how its going to be linked into the kernel:
Y: The feature or driver will be compiled into the kernel image and will be available at boot time
N: The feature or driver will not be compiled at all
M: The feature or driver will be compiled as a loadable module separate from the kernel image that can be loaded and unloaded at runtime.

<*> GPIO-based I2C arbitration
<M> GPIO-based I2C arbitration
<M> General Purpose I2C multiplexer (NEW)

As can be seen from the picture above (taken from menuconfig, a terminal-oriented configuration tool) First feature is enabled and will be built into the kernel Second feature is enabled and will be compiled separately as a loadable module
Third feature is disabled and will not be included in the
kernel