dts: arm: stm32f{2,4,7}: fix device tree warning

Switch the interrupt controller address to lower case to avoid this
warning:

  stm32f723e_disco.dts.pre.tmp:97.39-102.5: Warning (simple_bus_reg):
  /soc/interrupt-controller@40013C00: simple-bus unit address format
  error, expected "40013c00"

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>