cpu: stm32f2: fix linker-script to default map (flat ROM).
cpu: stm32f2: fix linker-script to default map (flat ROM).

Signed-off-by: Takeyoshi Kikuchi <af72ecfe6d0bf60ad0be9363518c74b6bed5ff74@centurysys.co.jp>
(cherry picked from commit 88915611c21ec1dac5c7e4594f6d58d4e2c9d885)

centurysys/RIOT,centurysys/RIOT,centurysys/RIOT,centurysys/RIOT,centurysys/RIOT,centurysys/RIOT