Added flash_fixup_stm to fix geometry reversal on STMicro M29W320ET flash chip.

Modeled after flash_fixup_amd, this patch handles the geometry reversal
or erase sectors that exist for ST Micro (now Numonyx) M29W320ET flash.
Since I cannot test all STM's chips, the detection is implemented as
narrow as possible for now.

Signed-off-by: Richard Retanubun <RichardRetanubun@RuggedCom.com>
Signed-off-by: Stefan Roese <sr@denx.de>