ARM: dts: stm32mp13: remove shmem for scmi-optee

CFG_STM32MP1_SCMI_SHM_SYSRAM will be disabled by default for STM32MP13x
SoCs in next OP-TEE version and the OP-TEE SMCI server uses the OP-TEE
native shared memory registered by clients.

To be compatible by default with this configuration this patch removes
the shared memory in the SCMI configuration and the associated reserved
memory in SRAM.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>