remoteproc: stm32: Allow hold boot management by the SCMI reset controller

The hold boot can be managed by the SCMI controller as a reset.
If the "hold_boot" reset is defined in the device tree, use it.
Else use the syscon controller directly to access to the register.
The support of the SMC call is deprecated but kept for legacy support.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20230512093926.661509-3-arnaud.pouliquen@foss.st.com