Supporting new flash in pflash

[Joel Stanley]

> On Wed, 2015-11-18 at 17:23 +1030, Joel Stanley wrote:
>> root at barreleye:~# ./pflash -i -b
>> LIBFLASH: Failed to set controller 4b mode
>> LIBFLASH: Flash configuration failed
>> Failed to open flash chip

The error message was due to libflash/pflash not supporting 4b mode
when talking to the BMC flash. It wasn't actually failing, the code
was intentionally not entering 4b mode as it thought it was
unsupported.

With Ben's help we discovered the BMC bus needed the SPI Address Cycle
Selection bit in FMC04 set in order to enter 4b mode. I have fixed
this in my branch on Github:

 https://github.com/shenki/skiboot/commits/barreleye-pflash

I will finish these patches off tomorrow and submit them to the
skiboot tree. From there we can pull in a new pflash build into
OpenBMC, and be able to flash our BMC from under Linux.

I tested it on both a Palmetto and a Barreleye tonight, and didn't
create any bricks, so feel free to give it a spin if you need it
before it hits the official builds.

Cheers,

Joel