stm32mp15: replace CONFIG_TFABOOT when it is possible

stm32mp15: replace CONFIG_TFABOOT when it is possible

In some part of STM32MP15 support the CONFIG_TFABOOT can be replaced
by other config: CONFIG_ARMV7_PSCI and CONFIG_ARM_SMCCC.

This patch also simplifies the code in cpu.c, stm32mp1_ram.c and
clk_stml32mp1.c as execution of U-Boot in sysram (boot without SPL and
without TFA) is not supported: the associated initialization code is
present only in SPL.

This cleanup patch is a preliminary step to support SPL load of OP-TEE
in secure world, with SPL in secure world and U-Boot in no-secure world.

Reported-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>