mips: fix cpu_reset memory leak

Remove cpu_mips_register()
- move mmu_init(), fpu_init() and mvp_init() into cpu_mips_init()
- move the other parts in cpu_mips_init()

Reported-by: Blue Swirl <blauwirbel@gmail.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
