CFI: allow for dynamically determined flash sizes and addresses

The CFI driver allowed only for static initializers in the
CFG_FLASH_BANKS_LIST definition, i. e. it did not allow to map
several flash banks contiguously if the bank sizes were not known in
advance, which kind of violates U-Boot's design philosophy.

(will be used for example by the TQM8xxL boards)

Signed-off-by: Wolfgang Denk <wd@denx.de>