ARM: stm32: Initialize TAMP_SMCR BKP..PROT fields on STM32MP15xx

ARM: stm32: Initialize TAMP_SMCR BKP..PROT fields on STM32MP15xx

In case of an OTP-CLOSED STM32MP15xx system, the CPU core 1 cannot be
released from endless loop in BootROM only by populating TAMP BKPxR 4
and 5 with magic and branch address and sending SGI0 interrupt from
core 0 to core 1 twice. TAMP_SMCR BKP..PROT fields must be initialized
as well to release the core 1 from endless loop during the second SGI0
handling on core 1. Initialize TAMP_SMCR to protect the first 32 backup
registers, the ones which contain the core 1 magic, branch address and
boot information.

This requirement seems to be undocumented, therefore it was necessary
to trace and analyze the STM32MP15xx BootROM using OpenOCD and objdump.
Ultimately, it turns out that a certain BootROM function reads out the
TAMP_SMCR register and tests whether the BKP..PROT fields are non-zero.
If they are zero, the BootROM code again waits for SGI0 using WFI, else
the execution moves forward until it reaches handoff to the TAMP BKPxR 5
branch address.

This fixes CPU core 1 release using U-Boot PSCI implementation on an
OTP-CLOSED system, i.e. system with fuse 0 bit 6 set.

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