scripts: gen_handles.py: take device start symbol as argument.

The current gen_handles.py script uses linker defined symbols.
As preparation for support of more linkers the gen_tables.py now takes
the device start symbol as argument.

For example, armlink and ld uses different symbols.
With ld those can be named explicitly, but for armlink the linker
decides the names.

For ld, Zephyr defines: __device_start
For armlink, the symbol is defined as: Image$$<section name>$$Base

Therefore knowledge of the linker symbol to be used must be passed to
gen_handles.py so that the correct symbol can be used for locating
devices.

To support this change, the creation of the asm, compiler, compiler-cpp,
linker targets has been moved from target_toolchain_flags.cmake to
target_toolchain.cmake.

All linkers has been updated to support the use of the
device_start_symbol on the linker target.

List of linkers updated:
- ld
- lld
- arcmwdt

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>

CMakeLists.txt

@@ -795,6 +795,7 @@ if(CONFIG_HAS_DTS)
     --output-source dev_handles.c
     --kernel $<TARGET_FILE:${ZEPHYR_PREBUILT_EXECUTABLE}>
     --zephyr-base ${ZEPHYR_BASE}
+    --start-symbol "$<TARGET_PROPERTY:linker,devices_start_symbol>"
     DEPENDS ${ZEPHYR_PREBUILT_EXECUTABLE}
     )
   set_property(GLOBAL APPEND PROPERTY GENERATED_KERNEL_SOURCE_FILES dev_handles.c)