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