dts: arm: st: h7rs: Increase memory size of sram0

The h7rs option byte default setting configures the AXI SRAM1-4 as one
contiguous memory, sram0 can therefore be increased to 456k (3x128k + 72k).
The .yaml files of the boards nucleo_h7s3l8 and stm32h7s78_dk are adjusted
accordingly.

Signed-off-by: Thomas Decker <decker@jb-lighting.de>