ARM: dts: stm32: Drop access-controllers from SPL DT on DH STM32MP15xx DHSOM

The access-controllers DT property is not useful in STM32MP15xx SPL,
remove it to reduce SPL control DT size. No functional change.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>