Retrieve RAM base address from DT instead of using STM32_SDRAM_FMC

For STM32F7, FMC block base address is 0xA0000000, but SDRAM
registers are located at offset 0x140 inside FMC block.
Update the stm32_fmc_regs fields with all FMC registers
to map SDRAM registers at the right address.

These additionals registers will be used later.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>

Migrate all FMC defines from arch/arm/include/asm/arch-stm32f7/fmc.h
to drivers/ram/stm32_sdram.c

This will avoid to add an additionnal arch-stm32xx/fmc.h file when
a new stm32 family soc will be introduced.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Vikas Manocha <vikas.manocha@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

If CONFIG_CLK flag is not set, compilation raises the
following error message:

drivers/ram/stm32_sdram.c: In function 'stm32_fmc_probe':
drivers/ram/stm32_sdram.c:154:2: error: 'ret' undeclared (first use in this function)
  ret = stm32_sdram_init(dev);

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
cc: Vikas Manocha <vikas.manocha@st.com>

At present devices use a simple integer offset to record the device tree
node associated with the device. In preparation for supporting a live
device tree, which uses a node pointer instead, refactor existing code to
access this field through an inline function.

Signed-off-by: Simon Glass <sjg@chromium.org>

Actually the sdram memory on stm32f746 discovery board is micron part
MT48LC_4M32_B2B5_6A. This patch does the modification required in the
device tree node & driver for the same.

Also we are passing here all the timing parameters in terms of clock
cycles, so no need to convert time(ns or ms) to cycles.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
cc: Christophe KERELLO <christophe.kerello@st.com>

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
cc: Christophe KERELLO <christophe.kerello@st.com>

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
cc: Christophe KERELLO <christophe.kerello@st.com>

This patch also removes the sdram/fmc clock enable from board specific
code.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
cc: Christophe KERELLO <christophe.kerello@st.com>

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
cc: Christophe KERELLO <christophe.kerello@st.com>

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
cc: Christophe KERELLO <christophe.kerello@st.com>