Move the syscall_handler.h header, used internally only to a dedicated
internal folder that should not be used outside of Zephyr.
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
In order to ease user thread testing with fuel gauges, enable syscalls for
the fuel gauge emulator backend API.
Signed-off-by: Aaron Massey <aaronmassey@google.com>