dts: arm: st: Fix memory mapping and size for STM32L47x/8x/9x/ax

Split and fix the total SRAM size for STM32L47x/L48x/L49x/L4Ax
device. Those MCUs with up to 320 Kbytes SRAM:
• 96 Kbytes SRAM1 and 32 Kbyte SRAM2 on STM32L47x/L48x.
• 256 Kbyte SRAM1 and 64 Kbyte SRAM2 on STM32L49x/L4Ax
The sram0 node at address 0x20000000 and sram1 at address 0x10000000

Signed-off-by: Francois Ramu <francois.ramu@st.com>