The USB stack can callback a driver is about to be reset by an
external entity and right after it, so the driver can save state and
then restore it.

This commit implements said support; it is implemented actually in the
core, bus-generic driver [i2400m_{pre,post}_reset()] and used by the
bus-specific drivers. This way the SDIO driver can also use it once
said support is brought to the SDIO stack.
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>