ARM: stm32: fix PRE_CON_BUF_ADDR on STM32MP13

ARM: stm32: fix PRE_CON_BUF_ADDR on STM32MP13

Since SYS_MALLOC_F_LEN increasing to 0x2100000 on STM32MP13, the
pre-console buffer is overlapped by stack (0xC0400000 + 0x2100000),
so the this buffer must be moved just before the bootstage to avoid issue.

After this patch the pre-relocation memory mapping for STM32MP13x is:

C3000000	= Bootstage	CONFIG_BOOTSTAGE_STASH_ADDR
C2FFF000	= PreConsole	CONFIG_PRE_CON_BUF_ADDR
           with size CONFIG_PRE_CON_BUF_SZ = 4096
C0400000	= start for stack	with CONFIG_CUSTOM_SYS_INIT_SP_ADDR
           including CONFIG_SYS_MALLOC_F_LEN
C0000000	= Load Address of U-Boot	with CONFIG_TEXT_BASE

Fixes: 93c962c7af7e ("configs: stm32mp13: increase SYS_MALLOC_F_LEN to 0x210000")
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>