spiflash: Add spiflash_set_protection

Some SPI FLASH devices start with block protection set.
spiflash: Remove capacity_to_bytes

Unfortunately this isn't nearly as standardized as I was hoping. In
fact, not all devices even seem to report capacity in READ_ID.
Merge branch 'master' of https://github.com/mchck/mchck
Re-add LLWU and SMC to linker K20 script

It seems these were dropped in the recent refactoring
Merge pull request #98 from bgamari/master

spiflash: Add spiflash_set_protection
toolchain: remove i2c stop flag

Turning off the bus master when there are things left to transmit didn't
work out, and the way I read the spec, repeated START is completely and
utterly the same as STOP followed by START. Some devices might not treat
them the same, but I'd say they violate the spec, so we'll see if we
encounter that.