Create more suitable Raspberry Pi 2 overclock settings.

[JaapKeuter]

First off there is no reset to default, so adding a Pi2_None option to
go back to those.

Second, furhter research(*) has shown that slightly lower settings do
not cause stabilty problems versus the current overclock settings.
Renaming this modest overclock settings due to lack of overvoltage.

(*) http://linuxonflash.blogspot.nl/2015/02/a-look-at-raspberry-
pi-2-performance.html

[AnAkkk]

Ignore my previous posts.
Some more tests on my Pi 2 show that I need 2 overvolt (I guess you shouldn't set it to 0) with that overclock setting otherwise I get random lockups and I always seem to get some errors in memtester, no matter the SDRAM setting.

From my tests, this config seem to work fine fine for me:
1000MHz ARM, 500MHz core, 480MHz SDRAM, 2 overvolt
Changing SDRAM to 490 or more produces errors.

EDIT:
After running it more times I could actually reproduce the errors even with 480MHz, although it's rarer than 490, but it still happens...

[JaapKeuter]

So, you say: set overvolt to 2, i.s.o. 0? Even though that's not what is in the test results, I've been running my Pi2 at the 2 overvolt setting 24/7 for well over two months now without problems, so maybe it is the right setting.

Btw: Maybe you should test with 483 MHz i.s.o. 480 MHz. Maybe that matches better with the SoC internals.

[AnAkkk]

What does "i.s.o" means?
Anyway, overclock 2 is fine. I just had some random lockups due to the SDRAM setting, which also produces errors in memtester. According to various forum posts I could read on raspberry official forum, other people have the same issue as well.
I had to set it to 460 or 470 MHz (can't remember which one, can't check right now) to not have any errors.

[JaapKeuter]

i.s.o.= instead of
By the way, now you say 'overclock 2 is fine', I guess you meant to say 'overvolt 2 is fine'.
Maybe an additional setting should be defined to set a lower frequency.

[AnAkkk]

Yes sorry, I meant overvolt 2.
Anyway there has been no commit since January, I'm not sure if this will get merged anytime soon...

[dankcushions]

Pi2 overclock preset SDRAM speed is INCREDIBLY aggressive. this might not be a problem for most applications but for games/emulation it'll quite likely cause a Pi2 to crash. 483 is the highest I can get to.