MIPS: Share generic kernel code with other architecture

Some architectures might seek to utilize a significant portion of the
generic kernel code while maintaining independence from the generic
kernel due to specific peculiarities.

This patch allows for the reuse of core code, preventing unnecessary
duplication.

Suggested-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>