cpufreq driver for LGR

[nickdesaulniers]

sincw LGR has 2 operating modes (PDN_LGR_SOCMODE), a cpufreq driver would help save battery life.

[Wolfvak]

I've actually discussed it with @profi200 and he says we can actually put the new3DS SoC into the "LGR1+536MHz" mode and still use both the L2C and extra CPUs but running at 536MHz, so we get 3 operating points in total. Not sure it'd help a lot with the battery but the kernel seems to be getting smarter and smarter about saving power with those.