various minor cleanups

Remove unused assembly routines "secure_mmu_xxx".

arm32/plat-stm:  move platform stm definitions of CFG_TEE_xxx configs
from conf.mk system_config.in

Remove obsolete unmaintained support for SIGNTOOL for TA signatures.

Removed deprecate marcos/make variables:
_USE_SLAPORT_LIB, CORE_MEM_UNSAFE, TEE_ACCEPT_UNSIGNED_BINARIES,
ACCEPT_UNSIGNED_BINARIES, SIGNTOOL, LOCAL_SIGNKEYSANDPACKAGESROOT,
LOCAL_SIGNPACKAGEROOT, TA_SIGN_BINARY, 8540APE, ORLY_LX,
DEFAULT_TA_SSWNAMES, SSWNAMES.

Lower somewhat verbosity at TA build.

Change-Id: I8e33879ce7f2bebe4bf600510d01d07a0324e6df
Reviewed-on: https://gerrit.st.com/14175
Reviewed-by: Etienne CARRIERE <etienne.carriere@st.com>
Tested-by: Etienne CARRIERE <etienne.carriere@st.com>
This comment is just a personal reminder, please remove it.