mtd: cfi - if defined, use MAX_FLASH_BANKS_DETECT for static declarations

a.k.a cfi_mtd.c does as cfi_flash.c does.  This also prevents
the TQM834x build from doing a:

cfi_mtd.c:36: error: variably modified 'cfi_mtd_info' at file scope
cfi_mtd.c:37: error: variably modified 'cfi_mtd_names' at file scope

using gcc 4.4.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Stefan Roese <sr@denx.de>