Audit <flash.h> inclusion

A large number of files include <flash.h> as it used to be how various
SPI flash related functions were found, or for other reasons entirely.
In order to migrate some further CONFIG symbols to Kconfig we need to
not include flash.h in cases where we don't have a NOR flash of some
sort enabled.  Furthermore, in cases where we are in common code and it
doesn't make sense to try and further refactor the code itself in to new
files we need to guard this inclusion.

Signed-off-by: Tom Rini <trini@konsulko.com>