spi: Add spi_is_idle

This allows us to safely determine when it's safe to sleep the core
spiflash: Remove spiflash_is_idle

This wasn't safe
usb: Enable RESUME support

This allows capable firmware to enter sleep modes which de-clock the USB
module.
Merge branch 'master' of https://github.com/mchck/mchck
Merge branch 'master' of https://github.com/mchck/mchck
Merge branch 'master' of https://github.com/mchck/mchck