ram: stm32_sdram: Adds stm32f429-disco fixes for HardFault at booting

- adds reading FMC swap setting from DTB to SDRAM driver
- sets FMC swap for stm32f429-disco board
- changes ram start address to 0x90000000

Signed-off-by: Radoslaw Pietrzyk <radoslaw.pietrzyk@gmail.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>